Introduction 

Body recomposition describes the process of reducing fat mass while simultaneously increasing lean muscle.  Body recomposition changes have been well documented in the scientific literature, yet many people remain skeptic arguing that to lose fat mass, the body must remain in an energy deficit (i.e. eating fewer calories relative to maintenance), and to increase lean muscle, the body must be in an energy surplus (i.e. consuming more calories relative to maintenance).  Ultimately, those that believe it is not possible to lose fat while increasing muscle, argue body recomposition defies the law of thermodynamics.  This article will discuss how it is possible to achieve simultaneous improvements in lean muscle while losing fat, as well as provide scientific support for body recomposition in trained and untrained populations, both under overfeeding (i.e. caloric surplus) and underfeeding (i.e. caloric deficit) conditions.

How Is Body Recomposition Possible?

To understand how body recomposition is possible, it is relevant to review the first law of thermodynamics, a fundamental law in physics that describes the movement of heat and energy in the body [5, 3].  The first law of thermodynamics states that energy cannot be created or destroyed, only changed [3].  For example, consuming more calories than maintenance calorie level (i.e. the calories consumed to maintain stable weight), changes the energy in the body to store more energy.  Conversely, reducing the energy stored by the body results from consuming fewer calories relative to those consumed at maintenance level.  To simplify further, if the body is in negative energy balance, the body will reduce its own energy and when the body is in positive energy balance, it will store energy.  

It is, however, incorrect to assume that negative energy balance will result in lowering bodyweight.  Weight change can still occur without changing the amount of energy stored or expended.  For example, weight change can occur through fluctuations in water intake from reducing certain foods [6].  As each gram of stored carbohydrate (glycogen) carries 3-4 grams of water, reductions in glycogen storage from reducing carbohydrates would lower total bodyweight, but without changing total energy balance [6].  Therefore, energy balance and weight change should be viewed as separate components as it is possible to lose body mass without losing stored energy.

It has been proposed that body recomposition is possible through a process known as calorie partitioning, whereby calories can be independently used for either increasing muscle building or fat mass.  This process, expressed as a P-ratio in research, indicates the portion of lean mass lost, or gained, for every unit of body weight change [5].  Evidence of P-ratio dates back to the research of Dr. Gilbert Forbes in the 1980’s.  In his research, Forbes found that overfeeding subjects by 1,195-1,1783 calories per day for 17-21 days resulted in 3.5-5.8 kg of bodyweight [4].  The author found that overfeeding, expectably, induced weight gain, but surprisingly a substantial portion (51%) of the subjects weight gain came from lean body mass [4].  Forbes found the average composition of the weight gain among subjects was 44% lean body mass 56% fat mass [4].

Body Recomposition: Overfeeding Plus Resistance Exercise

To better understand the body’s capacity for calorie partitioning and body recomposition under exercise conditions like gym sessions with a personal trainer, a number of studies reveal improvements in lean body mass and simultaneous reductions in fat mass when individuals are either in a calorie surplus or deficit and engaging in resistance exercise.  

Spillane and Willoughby (2016) randomised 21 resistance-trained males to either protein plus carbohydrate (HPC) group or a (HC) carbohydrate supplement group and placed them through an 8-week resistance exercise program [8].  Both the HPC and HC groups were overfed 1,394 and 1,101 calories above their current daily caloric intake, equating to a total of 3,700-3,800 calories per day [8].  

The HC group received a maltodextrin carbohydrate supplement of 312 grams (1,248 calorie) per day, while the HPC group received an equivalent 312 gram (1,248) supplement, but comprised of whey protein (94g protein, 196g carbohydrates, and 22g fat) [8].  

Participants engaged in a 4-day per week resistance exercise program that was split into two upper body and two lower body sessions for 8-weeks [8].  Within each exercise, participants completed 3 sets of 8-10 repetitions using 70 – 80% repetition maximum [8]. 

Results showed that the HC group had a P-ratio of 14% lean body mass and 86% fat mass, while the HPC group had a P-ratio of 59% lean body mass and 41% fat mass [8].  These P-ratio’s translated in to a  2.28kg increase in lean body mass in the HPC group and a .25kg increase in lean body mass in the HC group [8].  Findings from this study suggest that additional calories in excess of daily caloric intake could result in improved lean body mass when performing resistance exercise and protein intake is maintained at 2.4g/kg/day [8].

Another study by Antonio and colleague (2015), demonstrated the potential for body recomposition during an calorie surplus combined with progressive resistance exercise [1]. In their study, the authors assigned 73 resistances trained men and women to either a “normal protein” (NP) or “high protein group” (HP) [1].  The NP group was asked to maintain their current dietary habits, while the HP group was prescribed a 3g protein per kilogram per day [1].  Participants in the NP group increased their daily calories by approximately 100 calories per day from about 2,016 to 2,119 calories, on average [1].  Participants in the HP group increased their daily calories by about 370 calories per day from about 2,240 to 2,614 calories, on average [1].

Subjects kept a food diary using MyFitnessPal for dietary adherence and evaluation [1].  The resistance exercise program was completed 5 days per week for 8-weeks [1].  A split routine was utilised whereby participants worked different muscle groups on consecutive days [1].  The authors used BodPod air displacement to evaluate body composition changes [1]. 

Results of this study showed that fat free mass, which encompasses muscle, increased similarly in both groups by an average of 1.5kg from baseline [1].  However, participants in the NP group increased fat mass, on average, by 0.3kg from pre to post-study, while participants in the HP group lost fat mass, on average, by 1.6kg [1].  Also, body fat percentage reduced in the NP group by 0.6%, while participants in the HP group 2.4% over the 8-week period [1]. This would lend further support to the capability of body recomposition in an energy surplus when performing resistance exercise and protein intake is elevated [1].

Body Recomposition: Underfeeding Plus Resistance Exercise

Demling and DeSanti (2000) published a study in the Annals of Nutrition & Metabolism that compared the effects of combining 12-weeks of resistance exercise with a high protein diet against dieting alone on body composition change [2].  In their study, 38 untrained, male, overweight (23 – 35% body fat) police officers were randomised to either a diet group (250 calorie deficit), a diet plus resistance exercise plus casein protein (1.5g/kg/day) group, or a diet plus resistance exercise plus whey protein (1.5g/kg/day) group [2].  

Participants performed 30-35 minute resistance exercise workouts 4-days per week using resistance machines for all major muscle groups (i.e. legs, shoulders, back) [2].  Subjects could also choose to perform aerobic./cardiovascular exercise on non-training days, however this was not required [2].  Body composition was measured using skin fold callipers [2].  

Following 12-weeks, weight loss was approximately 2.5kg in all three groups [2].  Body fat in the diet alone group decreased from 27% to 25% [2].  Body fat in the diet, exercise and casein protein group decrease from 26% to 18% [2].  Finally, body fat in the diet, exercise and whey protein group decreased from 27% to 23% [2].  Lean mass remained unchanged in the diet group, while individuals in both the casein and whey protein plus exercise groups increased their lean body mass by 4kg and 2kg from baseline [2].  Findings from this study lend support to the potential for body composition change under relatively low energy deficits (150-200 daily calorie deficit) [2].

Additional evidence exists that demonstrate, even under severe calorie deficits, body recomposition is possible [7].  A study in the American Journal of Clinical Nutrition in 2016 showed that even during marked energy deficit, body recomposition is still attainable [7].  In that study, the authors placed 40 overweight (BMI > 25), young men, through a 4-week study where they were allocated to either a control group (CON) or protein group (PRO) [7].  The CON group were placed in a 40% calorie deficit and prescribed 1.2 grams per kilogram of protein per day and a macronutrient composition of 15% protein, 50% carbohydrates, and 35% fat [7].  The PRO group were placed in a 40% calorie deficit as well, but daily protein doubled to 2.4 grams per kilogram of protein per day and a macronutrient composition of 35% protein, 50% carbohydrates, and 15% fat [7].

Each week, participants in both groups completed two full-body resistance exercise circuits (10 repetitions for 3 sets at 80% of one-repetition maximum), two sessions of slow-intensity and high-intensity training on a stationary bike, one session of cycle ergometer, one session of plyometric body weight circuits, and given a step target of10,000 steps per day [7].

Participants in both groups were provided with all meals and beverages [7].  Both groups received supplements, the PRO group receiving a whey protein supplement and the CON groups receiving a placebo drink [7].  To increase daily protein intake, subjects received 3 or 4 dairy-based beverages each day [7].  Dietary compliance was assessed daily weight monitoring, checklists and contact with subjects [7].  Body composition was assessed using BodPod, DEXA, and bioelectrical impedance [7].  

Following the 4-week intervention, lean body mass was unchanged in the CON group (0.1kg +/-  1.0kg), while lean body mass increased in the PRO group by 1.2kg +/- 1.0kg [7].  Additionally, both groups decreased fat mass, however fat mass losses were greatest in the PRO group (-4.8kg +/- 1.6kg) compared with the CON group (-3.5kg +/- 1.4kg) [7].  Results from this study indicate further the potential for body recomposition even under a large energy deficit. 

Summary

Body recomposition, the simultaneous increase in muscle and reduction in fat mass, is well documented in the scientific literature under conditions where individuals are performing resistance exercise and consuming higher (>1.6g g/kg/day) intake of dietary protein.  In accordance with the first law of thermodynamics, energy cannot be created or destroyed, only transformed from one form to another [3].  Although it is true that the body needs to be in an energy deficit to lose bodily energy and in an energy surplus to store body energy, both energy and mass are independent components.  As previously indicated, it is possible lose weight without losing bodily energy (i.e. water loss).  Also, research shows that energy can be extracted and deposited separately into either lean body mass (i.e. muscle tissue) or fat mass.  

Under non-exercising conditions, when subjects are overfed calories, research demonstrates that a large portion of weight gain comes from increased lean body mass and not solely fat mass [4].  When exercising (i.e. resistance exercise), a number of studies show a simultaneous reduction in fat mass and increased lean body mass.  This is evidenced both when individuals are kept in positive or negative energy balance.  Provided an individual is engaging in progressive resistance exercise and protein intake is maintained at about 1.6 g/kg/day, or potentially even higher under certain circumstances (i.e. energy deficit), it appears the body has incentive for recomposition.  Caution, however, would need to be applied when using a caloric surplus for body recomposition, as larger caloric surpluses (>15%) would negate fat loss efforts despite favouring lean body mass increases.  Although, evidence by Antonio et al. (2015) indicate this may not be the case if caloric surplus is achieved via protein supplementation (i.e. whey protein) as compared with obtaining protein from whole foods.

References:

[1] Antonio et al. 2015. A high protein diet (3.4 g/kg/dA high protein diet (3.4 g/kg/d) combined with a heavy resistance training program improves body composition in healthy trained men and women – a follow-up investigation) combined with a heavy resistance training program improves body composition in healthy trained men and women – a follow-up investigation. October. Vol.12, No.39. Journal of the International Society of Sports Nutrition.

[2] Demling, R. H. and DeSanti, L. 2000. Effect of a hypocaloric diet, increased protein intake and resistance training on lean mass gains and fat mass loss in overweight police officers. Vol.44, No.1, pp.21-29. Annals of Nutrition and Metabolism.

[3] Fine, E. J. and Feinman, R. D. 2004. Thermodynamics of weight loss diets. December. Vol.1, No.15. Nutrition and Metabolism. 

[4] Forbes, B. G. et al. 1986. Deliberate overfeeding in women and men: energy cost and composition of the weight gain. Vol.56, No.1, pp.1-9. British Journal of Nutrition. 

[5] Hall, K. D. 2008. Body fat and fat-free mass interrelationships. June. Vol.97, No.6, pp.1059-1063. British Journal of Nutrition. 

[6] Kreitzman, S. N. et al. 1992. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. July. Vol.56, No.1, pp.292S-293S. The American Journal of Clinical Nutrition.

[7] Longland, T. M. et al. 2016. Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. March. Vol.103, No.3, pp.738-746. American Journal of Clinical Nutrition.

[8] Spillane, M. and Willoughby, D. S. 2016. Daily Overfeeding from Protein and/or Carbohydrate Supplementation for Eight Weeks in Conjunction with Resistance Training Does not Improve Body Composition and Muscle Strength or Increase Markers Indicative of Muscle Protein Synthesis and Myogenesis in Resistance-Trained Males. March. Vol.15, No.1, pp.17-25. Journal of Sports Science and Medicine.

How often you should work each muscle group, formally referred to as “training frequency,” is an important variable in the context of resistance exercise for muscle development (hypertrophy) [7].   Although many individuals that perform resistance exercise tend to focus on the total number of sessions per week, training frequency describes the number of times a specific muscle group is worked over per week [7].  The most common approach people tend to apply with resistance exercise is to work a given muscle group once per week.  A survey completed by Hackett and colleagues (2013) revealed that among 127 competitive bodybuilders, approximately 69% worked a muscle group once per week and none reported using a training frequency of working a muscle group more than twice per week [3].  Although, older research by Schoenfeld and colleagues (2016) found that working a given muscle twice per week achieved superior muscle growth compared to once per week [7].  However, limited research on training frequency was available at that time.  To better understand how often you should work each muscle and the potential benefits of higher training frequencies, this article will explore the impact of different training frequencies on muscle protein synthesis (mps), weekly volume (sets per muscle group), and per workout volume distribution.

Training Frequency and Muscle Protein Synthesis 

Muscle protein synthesis is the process of building new muscle proteins and serves as an accurate proxy for gauging the effectiveness of the longer term impact of resistance training programs in the context of muscle development.  The question around how often you should work each muscle largely revolves around maximising mps response.  Research shows that mps will peak following a resistance exercise session between 5 and 24 hours, then begin to decline thereafter [2, 4, 5].  The idea is that, as muscle protein synthesis begins to decline around 24 hours post-workout, to time the next resistance exercise session to again peak mps.  

When examining whether mps response in beginners, or untrained, individuals differ from experienced or trained individuals, both appear to follow a similar time course.  The key difference appears to be that, among individuals new to resistance exercise, mps appears to be directed more towards muscle damage repair and not muscle building [1].  In support, a 2016 study by Damas and colleagues published in the Journal of Physiology showed that untrained lifters experienced the greatest levels of muscle damage in the first 10-weeks of a progressive resistance exercise program [1].  During this period, mps was its highest, but directed more to repairing damaged muscle [1]. However, by 10 weeks, muscle damage was significantly less and mps response was directed more towards muscle building [1].  

Findings from the above study suggest that for beginners, working a muscle group once per week may be sufficient as the recovery process is longer.  However, experienced individuals may benefit from higher training frequencies as the recovery process becomes shortened.  Notably, the authors found that mps response peaked at 24 hours post exercise and was still elevated at 48 hours following a workout implying that working a muscle group once every 2 or 3 days may be ideal [1, 5].

Training Frequency and Volume

How often you should work each muscle also influences volume of work. Volume is the number of repetitions and sets performed for a given muscle group [6]. Alternatively, volume load, or total volume, describes the number of repetitions x sets x load.  As muscle growth is dependent on the magnitude (intensity) of load and duration of stimulus (volume), it is widely accepted that volume is an important driver of muscle development.  A 2016 meta-analysis by Schoefeld and colleagues found that each additional weekly set performed, the percentage gain in muscle size would 0.38% [6].  When comparing weekly sets on muscle growth, the authors showed a distinct advantage to 10 sets or more compared with less than 10 sets per week [6].

Increasing training frequency can be used as a means to increase total weekly volume per muscle group and subsequently muscle growth.  Just by increasing the number of days a specific muscle is worked will increase total weekly volume.  For example, if currently performing 8 weekly sets for legs over two workouts, adding a third workout to complete 3 more sets for legs would increase the total number of sets for legs from 8 to 11.  According to the evidence, this volume increase would improve muscle development for that given muscle group.

A valid argument can also be made that just by distributing one’s current per workout volume over multiple days, it would conceivably increase total volume as well because sets would be performed under less fatigued conditions.  For example, if performing 4 exercises for shoulders in a single workout, it is likely that accumulating fatigue would result in a decrease in total work completed (i.e. less number of repetitions performed or less resistance used each subsequent exercise).  However, if the same 4 shoulder exercises were distributed across two workouts (i.e. two on each day), the completion of more repetitions and/or greater resistance would be probable because the exercises would be completed under less fatigued conditions.  

Training Frequency and Volume Distribution 

Research indicates there may be an upper limit to how many sets can be performed in a single session before a plateau in muscle protein synthesis occurs.  According to the literature, this upper limit appears to be in the range of 10-12 sets per given muscle group [2].  In support, Damas and colleagues (2019) published a study in the Journal of Applied Physiology where the authors took 20 resistance trained young men and placed them through an 8-week resistance training program [2].  Subjects completed two workouts each week and performed both the leg press and leg extension.  The authors found that 12 sets of legs (6 sets leg extension and 6 sets leg press) resulted in only small increases in muscle protein synthesis compared to 8 sets to failure (4 sets leg extension and 4 sets leg press) [2].  These findings suggest that individuals performing more than 10-12 sets per muscle in a single session may benefit from dividing up this volume across multiple workouts, as opposed to completing the work in a single session.

For example, an individual performing 4 exercises for shoulders for 3 sets in a single workout may benefit more from distributing these sets across two workouts (i.e. two shoulder exercises on two separate days), rather than performing all in a single session.  Applying a training frequency of two days allows for 6 sets of shoulders to be completed on each workout, which may prove more effective for maximising muscle protein synthesis.  Importantly, focus should still be placed on bringing individual sets closer to failure as well as ensuring sufficient rest between sets of about 2 minutes or more [6].

Summary

How often you should work each muscle (training frequency) describes the number of times a given muscle is worked over a week period.  Literature supports that for individuals new to resistance exercise, working a specific muscle group once or twice per week is likely sufficient as the recovery process for untrained individuals is longer.  However, with resistance training experience, the recovery process is shortened and a training frequency of two or more can be used to potentially enhance muscle growth.  As volume is a primary driver of muscle growth, working a muscle multiple times per week via higher training frequencies can be an effective strategy to accelerate muscle development, provided enough time is given to recovery.  Additionally, high training frequencies of 3 or more per week can be utilised as a tool to distribute per session volume if sets for a given muscle exceed 10-12 sets per workout.

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References:

[1] Damas et al. 2016. Resistance Training-Induced Changes in Integrated Myofibular Protein Synthesis Are Related to Hypertrophy Only After Attenuation of Muscle Damage. September. Vol.594, No. 18, pp. 5209-5222. The Journal of Physiology.

[2] Damas et al. 2019. Myofibrillar Protein Synthesis and Muscle Hypertrophy Individualized Responses to Systematically Changing Resistance Training Variables in Trained Young Men.  September. Vol. 127, No. 3, pp. 806-815. Journal of Applied Physiology.

[3] Hackett, D. A. et al. 2013. Training Practices and Ergogenic Aids Used by Male Bodybuilders. Vol. 27, No. 6, pp.1609–1617. Journal of Strength Conditioning Research.  

[4] MacDougall et al. 1995. The Time Course For Elevated Muscle Protein Synthesis Following Heavy Resistance Exercise. December. Vol. 20, No. 4, pp.480-486. Canadian Journal of Applied Physiology.  

[5] Phillips et al. 1997. Mixed Muscle Protein Synthesis And Breakdown After Resistance Exercise In Humans. July. Vol. 273 (1 Pt 1),  E99-107. The American Journal of Physiology.

[6] Schoenfeld, B. J. et al. 2017. Dose-Response Relationship Between Weekly Resistance Training Volume and Increases in Muscle Mass: A Systematic Review and Meta-Analysis. June. Vol. 35, No. 11, pp. 1073-1082. Journal of Sports Sciences.

[7] Schoenfeld, B. J. et al. 2016. Effects of Resistance Training Frequency on Measures of Muscle Hypertrophy: A Systematic Review and Meta-Analysis. November. Vol. 46, No. 11. pp.1689-1697. Sports Medicine.

A well-designed home workout is reliant upon manipulation of exercise variables to accelerate the desired muscular adaptation (i.e. muscle growth, strength, endurance).  As discussed in a previous article, these exercise variables include both quantitative variables, such as repetitions, sets, resistance, frequency and tempo, as well as qualitative variables, such as exercise selection [8].  The purpose of manipulating exercise variables for home workouts carries the same aim as in gym workouts: to create overload to force the body’s systems to adapt, thereby making improvements in the desired adaptation [5]. 

Importantly, manipulating exercises variables should be tailored according to individual requirements as research shows that individual response to the same exercise routine vary considerably between individuals [2].  To maximise the effects of a home workout, a number of strategies can be applied to improve workout individualisation and enhance motivation to exercise.  This article discusses 3 specific strategies including individualising home workouts, structuring workouts, and recording progress.

1. Reflect Your Objectives

First and foremost, a home workout should reflect the desired adaptation. In the context of muscle development (hypertrophy), exercises should be organised in hierarchal order that prioritise muscles of greatest interest [4]. For example, an individual interested in developing the quadriceps (front thigh) muscles should prioritise exercises that target these muscle early in the workout. Research shows that the performance of multi-joint exercises (i.e. squat, shoulder press, chest press) significantly decline when completed later in a workout following multiple exercises that stress the same muscle groups [4].  Therefore, placing these exercises early in the workout, ensures they can be completed with less fatigue, greater rates of force output, higher number of repetitions, and great amounts of weight [4]. 

Total volume (repetitions x sets x load) is shown to be a powerful driver of muscle growth [6].  As total volume is typically described per muscle group, per week period, assigning a weekly total volume to prioritised muscle groups is important for maximal results.  Selecting the amount of volume per muscle is highly individual [6, 7].  For untrained individuals, research shows that performing 2 sets per major muscle group (i.e. legs, shoulders, back) is more beneficial compared to 1 set [6].  However, for trained individuals, multiple sets, 20 sets or greater, per major muscle group, have been suggested [6].  

To maximise development of targeted muscles, weekly volume should favour these muscles over others.  Therefore, attention should be given to assigning more volume to prioritised muscles groups [4].  This can be achieved through manipulation of different variables, including increasing the number of repetitions, sets, exercises, or training frequency for targeted muscles. For structuring a home workout, distributing total weekly volume about equally across individual workouts through the week will help to facilitate recovery between workouts and ensure higher quality of sets within each workout.  For example, if the selected total number of weekly sets for quadriceps is 20 and an individual performs 3 workouts per week, volume can be distributed across the three days (i.e. Monday 7 sets, Wednesday 7 sets, Friday 6 sets).

2. Structure Your Home Workout

Structuring your home workout can help build effectiveness and efficiency into your exercise.  A structured home workout organises exercise variables (i.e. exercises, exercise order, sets, repetitions, rest intervals) into a plan prior to a workout, as opposed to selecting these variables during a workout (see Full Body Workout design below).  This can help make your workouts more efficient as the duration of your home workout is dictated by your plan, not by arbitrary time selection.  

Also, as progression towards the desired adaptation is strongly determined by careful manipulation of exercise variables, structured workouts allow for more objective programming changes to be made over time, which can be valuable for understanding the impact of your workouts.  Periodisation, defined as the planned manipulation of exercise variables in order to maximise a specific training adaption (i.e. muscle growth, strength, endurance), can be helpful in making methodical improvements in the desired goal, while minimising fatigue or overtraining [5].  

Periodisation is based on the General Adaptation Syndrome (GAS), a model that states that systems (i.e. human body), will adapt to any stressors (i.e. exercise) imposed upon it to meet the demands of these stressors [5].  Without changes in overload, there simply is no need for the body to adapt and progress will cease.  A periodised or planned workout program can help avoid this issue by changing the exercise variables to force adaption [5]. 

3. Record Your Progress

With progress being one of the greatest motivators in exercise, it’s no surprise that as personal trainers, we record the workouts of our clients to assess exercise progression to enhance motivation.  As humans, we are hard-wired for productivity because of the immediate satisfaction it brings [3].  When goals are achieved, the brain releases dopamine, a neurotransmitter that gives feelings of pleasure and contributes to enhanced motivation, memory, and attention.  Research conducted by behavioural scientist Francesca Gino showed that individuals who recorded and completed small tasks felt the highest level of motivation and job satisfaction compared to individuals who did not complete small tasks [3].  Gino noted that completing smaller tasks, as opposed to larger goals, creates a positive feedback loop that, in turn, enhances motivation to work hard moving forward [3].  

Recording your home workout begins with selecting a workout tracker.  This can be a digital tracker or simple notebook.  Whichever form, it should be quick and easy to use.  Depending on your objective(s) it is highly beneficial to indicate baseline figures in your workout tracker.  These can be bodyweight, circumference measurements, and/or skin fold calliper measurements for body composition objectives like weight loss.  For strength, recording load is relevant and for muscle growth (hypertrophy) recording total volume (repetitions x sets x load).  Workout records can be detailed or simplified, but should, at an essential level, indicate the exercise, load and number of repetitions and sets performed.

Here is a simple 3 steps process for creating effective workout tracking:

Step 1: Record the date and time of the home workout at the top of the page or screen.

Step 2: Outline the home workout to be performed using the following template:

[Exercise]  –  [Load]  –  [Sets]  x  [Repetitions]

Set 3: Write relevant notes that will help indicate progression for your next workout.  For example, indicating that you will transition from kneeling incline press-ups to kneeling standard press-ups next workout, or that another set will be performed in a specific exercise.

Summary

Making progress in home workouts requires a basic understanding of the fundamental principles of exercise.  The principle of overload is based on the GAS model, which states that the body adapts to exercise and overload is required to ensure adaption continues [5].  In home workouts, the aim should be manipulate exercise variables to create overload and force adaption [8].  The principle of individualisation states that manipulation in exercise variables should be adjusted according to individual needs [8].  

Given this, your home workout should be designed and adjusted to maximise your response in line with your objectives.  Structuring and recording your home workouts are simple and effective strategies that can be used to make objective changes to your exercise programming that translate into better results.  Tracking workouts can also help to enhance motivation in home workouts by revealing progress over time.  This is relevant as research indicates that motivation is linked to exercise adherence, where adherence is a critical factor in determining goal attainment [1].  

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References:

[1] Baz-Valle, E et al. 2019. The effects of exercise variation in muscle thickness, maximal strength and motivation in resistance trained men. Vol. 14, No. 12. PLoS ONE. 

[2] Bamman, M, M. et al. 2017. Cluster analysis tests the importance of myogenic gene expression during myofiber hypertrophy in humans. June. Vol. 102, No. 6. pp. 2232-2239.  Journal of Applied Physiology.

[3] Gino, F. and Straats, B. 2016. Your Desire To Get Things Done Can Undermine Your Effectiveness. Harvard Business Review. Taken From: https://hbr.org/2016/03/your-desire-to-get-things-done-can-undermine-your-effectiveness.

[4] Hoffman, J. R. 2012. NSCA’s Guide to Program Design. Utilise Proper Workout Structure and Exercise Order.  

[5] Lorenz, D. and Morrison, S. 2015.  Current Concepts in Periodisation of Strength and Conditioning for the Sports Physical Therapist. November, Vol. 10, No. 6, pp. 734-747. International Journal of Sports Therapy. 

[6] Schoenfeld, B. J. 2017. Dose-response Relationship Between Weekly Resistance Training Volume and Increases in Muscle Mass: A Systematic Review and Meta-Analysis. June. Vol. 35, No. 11, pp.1073-1082. Journal of Sports Sciences.

[7] Schoenfeld, B. J. 2016. Science and Development of Muscle Hypertrophy.  Champaign, IL. Human Kinetics. 

[8] Zatsiorsky, V. M. and Kraemer, W. J. 2006. Science and Practice of Strength Training. Champaign, IL. Human Kinetics. 

Introduction 

Home workouts have become an important lifestyle transition for many as a response to coronavirus lockdown.  For individuals with established workout routines, gym closures and limitations on outdoor exercise have forced people to adapt their exercise to a home setting.  With limited, if any, access to exercise equipment, transitioning from gym to home workouts can certainly offer its challenges in finding and progressing exercises.  For many individuals working remotely from home, or ceasing work completely, these current circumstances also open new opportunity to initiate exercise routines to improve health or fitness.  Whether the course of action is to continue already established workout routines, or initiate new exercise routines, these 4 home workout guidelines should be considered to ensure progress is made toward the desire objective. 

Home Workout Guidelines 

Guideline 1: Apply This Basic Exercise Principle

Basic exercise principles refer to fundamental concepts or laws in exercise that govern the way the body responds.  These concepts are rooted in human biology and remain unchanged regardless of the setting.  One of the most important exercise principles is called the principle of overload.  Overload refers to applying a load (i.e. stimulus) that is greater than the habitual level [6].  For positive physical or physiological change to occur, overload within an exercise must occur [6].  Overload can be achieved in multiple ways, including [5, 6]:

1. Increasing the amount of resistance 
2. Performing more repetitions
3. Performing more sets
4. Increasing range of movement 
5. Slowing the speed at which the exercise is performed or adding pauses
6. Changing the exercise completely 

When overload is applied, a positive adaptation occurs, whereby the body adjusts to the stimulus being imposed [6]. This adaptive response can result in the body becoming stronger, fitter, and more muscular.  If the stimulus being imposed (i.e. resistance, repetitions, sets) remains unchanged over time, there is no impetus for the body to adapt, therefore no physical or physiological improvement will ensue [6].  For home workouts, the principle of overload is still very much applicable.  Increasing the resistance of an implement such as a dumbbell or kettlebell may not be feasible if equipment is limited.  Therefore, applying other forms of overload may be required in home workouts, such as increasing the number of repetitions performed or range of movement within an exercise.

Guideline 2: Gradually Build Intensity of Effort 

Intensity of effort refers to the level of effort exerted in each set [3].  In the context of muscle development, research demonstrates that muscle can be gained by using either high repetitions (i.e. more that 20) or low repetitions (i.e. less that 6) as well as light weights or heavy weights [2, 3, 4].  The reasoning relates to muscle fibres and how muscle fibres are activated during exercise [2, 3].  In a previous blog post, the role of muscle fibre recruitment was discussed in more detail and shown to be critical in the context of muscle development. In that article, it was explained how muscle growth is predicated on the body’s ability to recruit as many muscle fibres as possible. This can be accomplished in two ways [3]:

1. Lift heavy weights
2. Perform repetitions to the point close to failure (the point where no more repetitions can be completed)

When heavy weights are lifted, defined by lifting 1-5 maximal repetitions in an given exercise, all muscle fibres are recruited because high amounts of force are required to lift the weight [3].  This explains why lifting heavy weights can be effective for developing muscle [2, 3, 4]]. With light or moderate weights, the closer the set is taken to failure, the more muscle fibres are recruited [3, 4].  This occurs because although force requirements are low to begin, force demands become greater when the set is performed closer to failure [3]. 

Also, to bring a set closer to failure, an exercise can simply be made more challenging.  To make an exercise more challenging, any of the overload options indicated in guideline 1 can be applied.  With home workouts, lifting heavy weights may not be appropriate, either because of restricted access to graduated resistance, or because of resistance training experience (i.e. beginner level).  However, performing more repetitions or sets, increasing range of movement, or manipulating tempo are all viable options for increasing intensity of effort within home workouts.

Guideline 3: Individualise Your Home Workouts

Another foundational and essential exercise principle is the the principle of individualisation [5, 6].  This principle states that each individual is different and individual responses to exercise will vary [5, 6].  The common practice of replicating exercise programs to achieve similar results generally prove unsuccessful.  A study by Bamman and colleagues (2007) published in the Journal of Physiology demonstrated the principle of individualisation [1].  In their study, 66 untrained, healthy adults underwent the same 16 week resistance training program [1].  All subjects completed 3 workouts each week and performed three exercises, including leg press, knee extension, and squats [1].  Each exercise was performed for 8 to 12 repetitions and each set taken to volitional muscular failure (i.e. high intensity of effort to failure) [1].  

The authors increased the resistance of each exercise if the subjects completed 12 repetitions for at least two of the three completed sets (i.e. progressive resistance) [1].  Muscle biopsies of both legs were used to determine muscle growth and taken at baseline and 16 weeks following completion of the protocol [1].  To understand the effects of the exercise program on each subject, results were stratified into three groups [1]:

1. High responders
2. Moderate responders 
3. Low responders 

Following the 16 week progressive resistance program, subjects experienced large differences in muscle growth [1].

1. High responders: 25% of subjects experienced ~50% hypertrophic response 
2. Moderate responders: 50% of subjects experience ~20% hypertrophic response 
3. Low responders: 25% of subjects experience minimal to no hypertrophy

Results of this study show that home workouts should be individualised to how an individual responds to the program.  To maximise results from home workout programs, individuals should consider making adjustments in exercises, total week training volume (repetitions and sets), intensity of effort, or exercise frequency.  

Guideline 4: Be Creative with Your Home Workouts 

Limited access to exercise equipment at home does not mean home workouts are ineffective.  In fact, many exercises performed in a gym can easily be adapted to the home environment with creativity.  Important to remember that exercise implements  (i.e. machines, free-weights, cables) are simply tools and that the adaptive response from exercise is not specific to the tool, rather how the tool is utilised.  The home setting offers a number of options for creating variety within home workouts.  The following exercise are some examples of gym exercises adapted for home workouts:

1. Bodyweight press-ups are an excellent substitute for a dumbbell, barbell or kettlebell chest press for working the chest (pectoralis), back of arms (triceps) and front of shoulders (anterior deltoid).  Press-ups are easily progressed, moving from a kneeling position, full range, to a deficit variation.
2. Bodyweight squats are effective for targeting primarily the front of the legs (quadriceps) with added activation of the bum muscles (glutes) and calves.  Bodyweight squats are easily progressed by using single leg, split squats, variations elevating the front or back leg, or using deficit split squats.
3. Bodyweight inverted rows replicate rowing movements in the gym such as cable, barbell and dumbbell rows. These are effective to targeting the back muscles (latissimus dorsi), as well as front arms (biceps brachii), and the muscles resting between the shoulder blades (scapular retractors).  Inverting horizontally underneath a table can provide a suitable implement that places the body in the correct positioning for inverted rows.  This exercise is easily progressed by moving from a knees bent, leg assisted position, to keeping the legs straightened, then to elevating the legs.
4. Bodyweight hip thrusts are effective for activating the bum muscles (glutes).  This exercise is best performed using a sofa or armchair.  Bodyweight hip thrust can be progressed by changing body position and using a single leg variation.  
5. Butterfly shoulder raises target the middle part of the shoulder (medial deltoid) and the upper neck muscles (upper trapezius) through a fuller range of movement compared to a traditional lateral shoulder raise.  Light resistance from soup cans provide a suitable implement to create overload through these working muscles.  Progressive overload can be achieved by gradually lifting heavier cans to increase resistance.

Summary

For people that use gyms or other fitness facilities for exercise, transition into home workouts may feel ineffective, primarily because of equipment limitations.  However, with some creativity and an important understanding of fundamental exercise principles, it is possible to still make progress at home.  Adaptation, whereby the body adjust to an imposed stimulus, is still the objective in home workouts [6]. In order to create an adaptive response, exercise overload needs to be applied [6].  With overload, the body will adapt to the stimulus imposed, and positive physical and physiological change will ensue [5, 6].  

There are a number of different ways overload can be applied [5, 6].  Applying different forms of overload should be used to increase intensity of effort, which is shown to be important in the context of muscle development [2, 3, 4].  Finally, home workouts should be individualised based on individual response and manipulation of exercise variables may be required to elicit a greater, more accelerated response [6].

For more information on our personal training services please click here to read more.

References:

[1] Bamman, M, M. et al. 2017. Cluster analysis tests the importance of myogenic gene expression during myofiber hypertrophy in humans. June. Vol. 102, No. 6. pp. 2232-2239.  Journal of Applied Physiology.

[2] Burd, N. A. 2010. Low-Load High Volume Resistance Exercise Stimulates Muscle Protein Synthesis More Than High-Load Low Volume Resistance Exercise In Young Men. PLoS One. August. Vol. 5, No. 8. e12033.

[3] Krieger, J. Weightology. 2019. Quantifying Hypertrophic Reps and Hypertrophic Volume Load. Taken From: https://weightology.net/the-members-area/evidence-based-guides/quantifying-hypertrophic-reps-and-hypertrophic-volume-load/

[4] Schoenfeld, B. J. 2016. Differential Effect of Heavy Versus Moderate Loads on Measures of Strength and Hypertrophy in Resistance-Trained Men. Journal of Sports Science and Medicine. December. Vol. 15, No. 4, pp. 715-722. 

[5] Schoenfeld, B. J. 2016. Science and Development of Muscle Hypertrophy.  Champaign, IL. Human Kinetics.

[6] Zatsiorsky, V. M. and Kraemer, W. J. 2006. Science and Practice of Strength Training. Champaign, IL. Human Kinetics. 

Basic Physiology of Muscle Growth

Muscle tone, formally called muscle hypertrophy, is an increase in the size of muscle tissue [3].  Exercise, specifically resistance exercise. in all its forms, has been demonstrated to increase muscle hypertrophy [3].  Muscle tone and development occurs when muscles are subjected to stress from resistance exercise eliciting an adaptive response [3].  Adaptation, whereby the body adjust to its environment, is a key feature of all living species [3].  In exercise, the body adapts to the stress (i.e. resistance) imposed on it by getting larger and stronger to better cope with this stimulus when exposed again [3, 7].  This adaptive response continues as long as the physical stress is regularly applied [7].  

For individuals new to resistance exercise, there is an initial period of skill acquisition and motor pattern learning [7].  During this phase, the body is learning the movement and gaining important coordination [6, 7].  As an exercise is learnt (skill acquisition), the movement progresses from being disorganised and uncoordinated to smooth and efficient [7].  This initial period of motor learning and skill acquisition is essential for muscle tone and development [7].  Improvement in exercise technique corresponds with greater force production within a given exercise, which in turn can result in more muscle growth [7].

Motor Unit and Muscle Fibre Recruitment

Muscle tone and development is predicated on the body’s ability to maximally recruit what are called motor units and their associated muscle fibres [6].  As our muscles are innervated by the nervous system, a motor unit is defined as an individual motor neurone stemming from the spinal cord and the muscle fibres it innervates [3].  Muscle fibres are the cells that make up muscle and can be broadly classified into type I and type II [3, 6].  Often referred to as slow-twitch, type I fibres are fatigue resistant and more suited to muscular endurance [7]. Slow-twitch fibres can endure repeated contraction, however have limited capacity to generate force [3, 7].  In contrast, type II fibres produce maximal force much quicker, making them well suited for muscular strength and power [3, 7].  However, despite their capacity to generate high amount of force, fast-twitch fibres fatigue easily [3, 7].   

Both slow and fast-twitch fibres have the capacity for muscle hypertrophy, however, fast twitch fibres are shown to have a greater capacity (approximately 50%) [7].  Almost all whole muscles in the body are comprised of a mixture of slow and fast-twitch fibres [6].  Given this, both types are important for maximising muscle tone [7].  

It is well documented that muscle fibre and motor unit recruitment follow what is called the size principle [3, 6].  The size principle states that the force producing capacity of a motor unit is related to its size [3, 6].  At low levels of force requirement, smaller, lower-threshold, and slower motor units are recruited first [3, 6].  As force requirements increase, progressively larger, higher-threshold motor units are recruited [3, 6]. For example, lifting a heavy weight requires large amounts of force and recruits a high number of motor units, both low and high-threshold.  Lighter weights, if not taken close to muscular failure or at the beginning of a higher repetition set, require lower force, therefore only a fewer number of smaller, lower threshold motor units are recruited.   

How Many Repetitions?

It has been shown that repetitions taken closer to failure, the point where the weight cannot be lifted anymore, generates more muscle growth than repetitions further from failure [2, 4].  This is due to muscle fibre recruitment [1, 4].  As previously indicated, more muscle fibres and motor units are recruited when lifting close to failure due to increased force demands [2, 3, 4].  Repetitions taken close to failure have been called “hypertrophic” or “stimulating” repetitions because of their importance in generating muscle growth [4].

The effect of repetitions taken closer to failure were demonstrated by Burd and colleagues in 2010 [2].  In their study, 15 healthy, recreational active men performed different levels of resistance using a machine leg extension performed single leg [2].  The three conditions were: 

1. 90% of maximum weight lifted taken to failure (90FAIL)
2. 30% of maximum weight lifted matched repetitions x load of 90FAIL (30WM) 
3. 30% of maximum weight lifted taken to failure (30FAIL)

The first protocol (90FAIL) used heavier weights and completed fewer repetitions and took their set to failure [2].  The second protocol (30FAIL) used lighter weights and completed more repetitions and also took their set to failure [2]. The third protocol (30WM) used the same lighter weight as the 30FAIL group, however the set was stopped when this group completed the same number of work (repetitions x load) as the 90FAIL group, not going to failure [2].

Results showed that both groups that took their sets to failure had superior muscle growth compared with the 30WM group [2].  This study showed that lifting to failure (or close to failure) is highly important to muscle tone.  Furthermore, the study showed that muscle growth can be achieved by using either light or heavy weights.

The Role of Fatigue In Muscle Tone & Development

The role of fatigue during exercise is an important factor within motor unit recruitment [1, 4].  Even under low loads (i.e. light resistance), when fatigue increases and the muscle gets closer to failure, more muscle fibres are recruited and with them, larger, higher-threshold motor units [1, 4].  Moreover, these larger, higher-thresholds motor units activate recruitment of fast-twitch fibres because of the increased need to generate more force [3, 6].  For example, for a given exercise, with light-to-moderate resistance the first several repetitions will likely feel light and require little force.  At this point, there is a low number of lower threshold, slow-twitch fibre recruited.  However, as the set continues, provided the lifter continues lifting the load, the resistance begins to feel heavier and force production needs increase in an effort to keep the resistance moving [6].  As this force production increases, not only are slow-twitch fibres recruited, but also fast-twitch fibres [6].  In the Burd (2010) study, the role of fatigue would explain why the 30FAIL group achieved maximal muscle fibre and motor unit recruitment similar to the 90FAIL despite lifting considerably different loads.

Low Versus Moderate-To-High Repetitions 

Furthermore, moderate-to-high repetitions taken close to failure elicit more muscle tone and development than lower repetitions because of increased time under tension [1, 4].  Keeping a muscle under tension for longer period of time (i.e. multiple repetitions) stimulates muscular adaption to a greater extent than shorter time periods [1, 4].  That means, performing one or two repetitions of a given exercise produces inferior levels of muscle growth compared to a set of multiple repetitions [4]. 

Schoenfeld and colleagues (2016) demonstrated this their study aimed at determining muscular adaptations differences between heavy and moderate load resistance exercise[ 5].  In their study, 19 males subjects with resistance training experience (4-5 years) were randomised to either a heavy or moderate exercise group [5].  The heavy group performed 2-4 repetitions, while the moderate group performed 8-12 repetitions [5].  Each set were taken to close to failure [5].  The subjects exercised 3 days per week for 8 weeks [5].  Both groups completed 7 exercises for the upper and lower body [5].  Muscle tone was determined using ultrasound imaging of the back of the arm, front of the arm, and outer thigh [5].  Results of this study showed greater increases in muscle growth in all three areas among subjects in the moderate group compared with heavy group [5].  

The superior muscle development experienced in the moderate group can be explained by increases in exercise training volume [5].  A dose-response relationship between total weekly volume per muscle group and muscle hypertrophy has been well established.  This means that, up to a certain point, the more volume (i.e. repetitions x sets) performed per muscle group, per week, the greater the muscle growth [5].  Although both groups completed sets close to failure, the total weekly exercise volume in the moderate group were more than double than the heavy group. 

Practical Application 

Muscle tone and development is dependent upon the ability to maximally recruit motor units and their associated fibres [6, 7].  There are two ways in which a high number of motor units can be recruited [4]: 

1. Increase the resistance  
2. Bring the muscle close to failure

Heavier weights, provided they are taken close to failure, will maximally recruit all available motor units and activate type I and type II slow and fast twitch fibres, although primarily type II fibres [6].  Lighter weights, taken close to failure, will similarly recruit all available motor units and both fibre types. Lighter weights accomplish this via the role of muscle fatigue and increasing force requirements as the muscles move closer to failure [1, 2].  Using moderate (i.e. 6-15) or high (i.e. 16>) repetitions have an advantage for muscle growth over lower repetitions (i.e. <5) because of the increased time the muscles are under tension and higher volume of work.  

It has been suggested that taking a given exercise 1-5 repetitions from failure elicits the same response as going to failure [1].  Therefore, going to absolute failure is likely not necessary.  Important to note, repetitions to stimulate muscle growth fall on a continuum [4].  Even repetitions completed much farther from failure will elect some hypertrophic response [4].  However, this response will be less than those repetitions taken closer to failure [4].  Also, important considerations in taking exercises close to failure are proper technique and exercise experience.  As the working muscles fatigue going closer to failure, it is imperative, from a safety and performance quality standpoint, to retain proper technique.  Moreover, individuals new to resistance exercise should prioritise skill acquisition in coordinating to exercises before gradually taking sets closer to failure.  

For more information on our personal training services please click here to read more.

References:

[1] Beardsley, Chris. 2018. What is Training Volume? Taken From: https://medium.com/@SandCResearch/what-is-training-volume-286b8da6f427

[2] Burd, N. A. 2010. Low-Load High Volume Resistance Exercise Stimulates Muscle Protein Synthesis More Than High-Load Low Volume Resistance Exercise In Young Men. PLoS One. August. Vol. 5, No. 8. e12033.

[3] Kenney, W. L. et al. 2012 Physiology of Sport and Exercise. 5th Ed. Human Kinetics.

[4] Krieger, J. Weightology. 2019. Quantifying Hypertrophic Reps and Hypertrophic Volume Load. Taken From: https://weightology.net/the-members-area/evidence-based-guides/quantifying-hypertrophic-reps-and-hypertrophic-volume-load/

[5] Schoenfeld, B. J. 2016. Differential Effect of Heavy Versus Moderate Loads on Measures of Strength and Hypertrophy in Resistance-Trained Men. Journal of Sports Science and Medicine. December. Vol. 15, No. 4, pp. 715-722.

[6] Schoenfeld, B. J. 2016. Science and Development of Muscle Hypertrophy.  Human Kinetics. Champaign, IL. 

[7] Schoenfeld. B. J. 2013. The MAX Muscle Plan. Human Kinetics. Champaign, IL.

Introduction

The Personal Trainer Collective Conference – Bath, UK – April 23-24, 2016

The personal trainer collective (PTC) conference held in Bath, England on April 23-24, 2016 hosted some of the most well-respected exercise professionals in evidence-based fitness.  In a previous post, we looked at content presented by Brad Schoenfeld and Alan Aragon.  This post will introduce the remaining two speakers, Bret Contreras and James Krieger along their topic presented with practical application.

Bret Contreras – “The Glute Guy”

Bret Contreras was one of the four speakers at the PTC conference and is widely recognised as a leader in evidenced-based fitness, particularly in the area of posterior chain muscle and strength development.  Contreras holds a Masters Degree from Arizona State University and a PhD in sports science from AUT University.  Contreras is heavily involved in exercise science research and has contributed to a number of popular publications including Men’s Health, Men’s Fitness, Shape, and Oxygen in addition to still presently operating as a personal trainer.

Squat Exercise Technique

On day 2 of the conference, Contreras reviewed technique for the primary powerlifts including the squat, deadlift and bench press in addition to examining more isolated, posterior chain exercises like the hip thrust and good morning.  In discussing technique for the squat, Contreras indicated that he utilises the dumbbell goblet squat as a primary exercise for teaching proper squatting mechanics.  Contreras was adamant that full squatting is superior to partial squats with respect to strength and muscular development.  The following are highlighted points made when performing a deep goblet squat:

Moderate Width Stance – A moderate width stance of about shoulder width or slightly less than shoulder width is maintained throughout the squat.

Foot Flare – Feet are turned outward slightly (approximately 30 degrees), which allow the hips to externally rotate (rotate outwards) and move more freely into the deep squat position.

Elbows Tucked – In a dumbbell goblet full squat, elbows are tucked around the dumbbell allowing for full clearance of the knees when descending into a full squat position.

Elbows Between Legs – In the bottom position of a dumbbell goblet full squat, the elbows fall in between the legs to maximise depth.

Spinal Position – A upright and neutral spine position is maintained throughout the entire range of a dumbbell goblet full squat.  The back should not be flexed or hyperextended.

Feet Cautions – When descending into the bottom position of a full squat, there is caution to prevent foot pronation (rolling onto the big toe side) or caving-in of the feet, which will cause unwanted medial or inward dipping of the knees.  Instead, balance should be maintain over the mid or whole foot and “pushing” through the heels when ascending from the bottom position.

Finish With Hips – In the last third of the squat range, the lift is completed with explosive hip extension that utilises the glutes and hamstrings to complete the movement.

Breathing – Breathing during the squat will vary depending on the load used.  For maximal lifting, a held breath with abdominal brace is used at the start of the repetition to create intra-abdominal pressure and stabilise the spine.  During sub-maximal, lighter load and generally higher repetition sets, breathing inward during the eccentric (lengthening) phase and outward during the concentric (shortening) phase is used.

Squat Exercise Anatomy And Mobility  

On day 2, Contreras touched on reduced immobility and individual anatomy and how both elements can influence squatting mechanics.  Specifically, Contreras talked about the requirement for sufficient ankle dorsiflexion during the full squat.  This ankle movement brings the foot upward toward the shin and is important for achieving a low squat position.  Insufficient ankle dorsiflexion typically leads to a compensatory pattern of foot pronation during the deep squat.  As a resolution for this deficit, it is common for personal trainers to prescribe ankle mobility exercises to restore ankle dorsiflexion in addition to elevating the heels or advocating lifting shoes with heel lifts.  However, resolution using ankle mobility exercises will not necessarily resolve the issue.

Contreras touched briefly on anatomy and its influence on squat mechanics.  Limited ankle dorsiflexion can certainly be contributed by reduced ankle mobility, weakness or shortening of certain relevant structures.  Or, it can be caused by anatomical structure whereby limitation is due to genetic formation of the ankle bones.  In this instance, ankle mobility, stretching or strengthening would not resolve the issue.

Similarly, if a client presents with an anatomically short tibia (shin bone) relative to their femur (thigh bone), this will naturally cause a greater forward lean during the squat.  Likewise, a disproportionally long relative femur length will lead to increased forward lean as well.   These clients will undoubtably struggle to achieve depth in their squat, but not at the detriment of range of movement in the knees or hips, but rather anatomical structure.  Tom Purvis’s video above explains this anatomical restriction well.

An individual that presents with proportionally long femur-to-tibia length in addition to a proportional torso will be anatomically optimal for squatting.  This client may still present with immobility issues, however structurally they are optimal for the movement.

Practical Application 

As personal trainers, we are responsible for our clients correct execution of each exercise.  Given this, it highly important to demonstrate each exercise to identify proper technique.  Often, verbal instructions are misinterpreted and can lead to increased injury risk for the client.  Verbal and tactile cues are often required to facilitate a clients proper execution of an exercise and these cues should be customised appropriately to the response of each client.

There are a number of technical elements personal trainers must be aware of when instructing the squat, or any complex exercise.  Acquiring correct knowledge of each exercise in addition to understanding possible compensatory patterns of movement are prerequisites for instructing proper technique.

Often, personal trainers fail to consider anatomical structure of their clients in the context of performing certain exercises like the squat and deadlift.  For some clients, anatomy may restrict movement and subsequently hinder performance of a given exercise and it is important for personal trainers to understand the client is not at fault.  Instead, more attention may be required to develop the exercise, or alternative exercises may be required to develop strength or hypertrophy in the targeted muscle groups.

James Krieger – “The Statistician”

James Krieger was one of four speakers that presented at the PTC conference.  Krieger is a well respected researcher, speaker and scientist in evidenced-based fitness, specialising in the area of weight management.  Krieger holds two Master’s degrees, one in Nutrition from the University of Florida, the other in Exercise Science from Washington State University.  He is a licensed nutritionist and the former head of research for weight-loss and obesity management for Microsoft.

On Day 1 of the conference, Krieger spoke about weight management and the critical role of non-exercise activity thermogenesis (NEAT) in weight loss.  In personal training, it is evident that many clients share the objective of weight loss.  As a pre-requisite for achieving this goal, it is imperative to understand that, in healthy adults, weight gain occurs when energy intake persistently exceeds energy expenditure [3].  The knowledge that increasing daily NEAT can directly mitigate the effects of increased calorie consumption and greatly contribute to weight loss is highly applicable for personal trainers and their clients.

Non-Exercise Activity Thermogenesis (NEAT)

NEAT is the energy expenditure of all physical activities outside that of volitional sporting-like exercise, sleeping or eating [1].  NEAT does not encompass going to the gym for a workout, but rather includes all activities of daily living including walking, climbing stairs, typing, fidgeting, muscle tone, and maintenance of posture [1].  NEAT may be easier to conceptualise by considering all movements to activities during work and leisure hours [1].

What is the Daily Energy Expenditure of NEAT?

In sedentary individuals, daily energy expenditure is approximately 15% [2].  In physically active individuals, total daily energy expenditure is approximately 50% or more [2].

Measuring Non-Exercise Activity Thermogenesis

Neat can be measured by one of two approaches:

1.  The first approach consists of measuring or estimating total NEAT.  Here, total energy expenditure is estimated, then from it, basal metabolic rate (BMR) plus thermic effect of food (TEF) is subtracted [2].

2.  The second approach is a factorial approach, whereby the components of NEAT are quantified, and the total NEAT is calculating by summing up these components [2].

• BMR is energy expended when lying at complete rest.  It is largely (80%) calculated using lean body mass  BMR = 25.3 x Lean Body Mass (kg) [5].
• TEF is energy expenditure associated with digestion, absorption and storage of food and represents approximately 10-15% of total daily energy expenditure [2].

Issues Measuring Non-Exercise Activity Thermogenesis 

There are a few issues which make measuring NEAT levels problematic.  First, the great variety of activities that encompass NEAT make it very challenging to define in terms of human energy expenditure [2].  Also, the time period of measurement needed to gain a representation of NEAT is not well understood. [2].  A measurement period of 7 days have been used to provide a representative assessment of NEAT for a given period (i.e. 3 or 4 months) [1].  However, this measurement period is only a rough estimation.

Weight Loss And Non-Exercise Activity Thermogenesis

The variance of NEAT among people can be substantial with as much as a 2000 kcal per day difference in energy expenditure [1].  Leisure activities alone, such as yard work, house cleaning or cycling after work, has the potential to impact total daily energy expenditure (TDEE) by up to 1000 kcal per day [1].  However, the most variance in NEAT levels between people is related to occupational differences [1].   Physical Activity Levels (PAL) values are commonly used to represent NEAT and is calculated by dividing TDEE by BMR [2].   For example, an office worker that performs sedentary desk work with a PAL of 1.6 and changes occupation to work in landscaping with a PAL of 2.4 could increase NEAT levels by 1200 kcal per day [2].

A study by Ravussin and colleagues (1986) demonstrated the high degree of variance in NEAT among individuals [4].  In this study, the authors confined 177 subjects (103 males, 74 females) individually to a constructed respiratory chamber [4].  The respiratory chamber was 3m long, 2.5m wide, and 2.5m high and furnished with a toilet, sink, sofa-bed, desk, char, table, television, radio and intercoms [4].  The chamber formed an open-circuit calorimeter where both oxygen consumption and carbon dioxide production of each subject could be continuously measured and fresh air could be continuously drawn through the chamber [4].

NEAT was assessed both by having subjects wear a wrist motion sensor and via motion sensors mounted in the chamber [4].  Each subject spent a total of 24-hours in the respiratory chamber [4].  The results showed that energy expenditure varied significantly in each individual from 138 to 685 kcal per day [4] and the variance in energy expenditure were due to variability in the degree of NEAT levels i.e. walking around within the chamber and fidgeting [4].

Interestingly, energy expenditure was greater among obese subjects at all times compared to those of thinner subjects [4].  This was due to the larger mass of active tissue and higher energy costs of NEAT among obese subjects [4].  The authors note that energy expenditure resulting from NEAT is “an important component in total 24-hour energy expenditure and therefore in energy balance” and, for recommendations of daily caloric needs, “more emphasis should be given to the level of general physical activity” [4].

In an attempt to understand the impact of NEAT on weight gain, Levine and colleagues (1999) measured changes in energy storage in individuals who were overfed for 8 weeks [3].  Sixteen non-obese adults (12 males and 4 females, 25 to 36 years of age) underwent measures of body composition and energy expenditure before and after 8 weeks of overfeeding 1000 kcal per day above their maintenance calories [3].  On average, subjects gained 4.7 kg over the 8 week study period and fat gains were the same in males in females [3].

The authors assessed basal metabolic rate and found that overfeeding increased BMR by an average of 5% accounting for 8% of the excess energy ingested [3].  Also, thermal effect of food was measured and found to increase by 14% with overfeeding, but did not correlate with fat gain [3].  Therefore, both BMR and TEF did not account for the large variability in fat gain among subjects [3].  Instead, the authors found NEAT to be the primary mediator of weight gain with overfeeding [3].

The average increase in NEAT (336 kcal per day) accounted for two-thirds of the increase in daily energy expenditure [3].  Changes in NEAT accounted for a 10-fold difference in fat storage that predicated resistance to fat gain with overeating.  Lower values of NEAT correlated with the greatest weight gain, while those with higher NEAT were able to dissipate the excess energy so that excess calories were not stored as fat [3].  The graph below (Graph C) show the linear correlation between increased fat gain (kg) and decreased NEAT levels [3].

Practical Application

With the great majority of personal training clients sharing the goal of weight loss, understanding areas that directly impact weight gain and weight loss are crucial to facilitating a pathway toward this objective.  In addressing the goal of weight loss, personal training focusses principally on progressive resistance and proper nutrition.  While addressing both these areas will make positive contributions to a clients weight loss, assessing NEAT will undoubtably contribute the most to increasing daily caloric expenditure.

More recently, the media have popularised the recommendation of achieving 10,000 steps per day as a marker for adequate general activity with expected health benefits.  This recommendation can be traced back to Japanese walking clubs and made popular by pedometer manufacturers [7].  However, presently, there is lack of direct evidence that accumulating  any number of steps/day is associate with weight loss or reduced mortality.  Although, previous studies have reported that 30 minutes of moderate physical activity (i.e. walking) equates to approximately 10,000 steps/day [7].

A study by Yamanouchi et al. (1995) showed that an exercise and diet group of individuals instructed to take 10,000 steps/day over a 6-8 week period lost an average of 7.7 kg (3.6 kg more than a control group averaging 4,000 steps/day) [8].  Although, the subjects in this study exceeded the set goal averaging >19,000 steps/day [8].  Still, normative data to date indicate that 10,000 steps is reasonable for healthy adults [6].  Although for low active populations, such as among the elderly and those living with chronic disease, incremental increases of 2,000 – 2,500 steps/day above 10,000 steps/day is recommended [6].

Many strategies for personal trainers exist to help promote increasing client NEAT levels.  Those include, but are certainly not limited to:

• Walk to work
• Walk during lunch hour
• Walk after dinner
• Set up treadmill in front of TV
• Take stairs instead of escalator or elevator
• Park farther from destination
• Walk to co-worker’s desk instead of emailing or calling them
• Get off a stop early and walk
• Walk the dog more frequently
• Purchase a pedometer or accelerometer to set daily step goals

Educating clients on NEAT and the importance of maintaining adequate daily general movement for goals including weight loss are highly important and an essential component of our personal training service.  In assessing NEAT, we use pedometers with our clients as a simple, yet effective, method for gathering information related to daily, general movement.  This information is then utilised in combination with structured exercise and nutrition to accelerate the process of goal achievement.

For more information on our services please click here to read more.

References:

1.  Levine, J. A. et al. 2006. Non-Exercise Activity Thermogenesis. The Crouching Tiger Hidden Dragon of Societal Weight Gain. Arteriosclerosis, Thrombosis, and Vascular Biology. April. Vol. 26, No. 4, pp. 729-736.

2.  Levine, J. A. 2004. Nonexercise activity thermogenesis (NEAT): environment and biology. American Journal of Physiology, Endocrinology and Metabolism. May. Vol. 285. No. 5. E675-685.

3.  Levine, J. A. et al. 1999. Role of Nonexercise Activity Thermogenesis in Resistance to Fat Gain in Humans. Science. January. Vol. 283, No. 5399, pp. 212-214.

4.  Ravussin, E. et al. 1986. Determinants of 24-hour energy expenditure in man. Methods and results using a respiratory chamber. The Journal of Clinical Investigation. December. Vol. 78, No. 6, pp. 1568-1578.

5.  Schuler, L. & Aragon, A. 2014. The Lean Muscle Diet. Rodale Inc. New York.

6.  Tudor-Locke, C. et al. 2011. How many steps/day are enough? For adults.  The International Journal of Behavioural Nutrition and Physical Activity. July. Vol. 8, No. 79, pp.1186/1479-5868-8-79.

7.  Tudor-Locke, C. & Bassett DR Jr. 2004. How many steps/day are enough? Preliminary pedometer indices for public health. Sports Medicine. Vol. 34, No. 1, pp.1-8.

8.  Yamanouchi K et al. (1995). Daily walking combined with diet therapy is a useful means for obese NIDDM patients not only to reduce body weight but also to improve insulin sensitivity. Diabetes Care. Vol. 18, No. 6, pp. 775-778.

Introduction

Core strengthening has become an area of increasing interest in fitness and rehabilitation circles because of the rising rate of exercise-related low back injuries. In fitness, we emphasise abdominal exercises to achieve a defined or toned stomach, but with little or any consideration of spinal stability.  Yet, the core is a major stabiliser of the body and spine during movement and particularly during dynamic resistnce exercises like squats, deadlifts and direct abdominal work.

Anatomy Of The Core

 The abdominals are just one component that makes up our core.  Additional structures that compose the core include the lumbar spine, back extensors, quadratus lumborum (side flexing muscle) and multi-joint muscles, namely, latissimus dorsi and psoas (primary hip flexor) that pass through the core, linking it to the pelvis, legs, shoulders, and arms.

If we consider the traditional approach to core strengthening, using a sit-up either on the floor or over gym ball, the repetitive movement here is spinal flexion.  Evidence clearly shows that the damaging mechanism leading to disc herniation, or prolapse of the spine, is repeated lumbar flexion requiring only very modest concomitant compressive spinal loads. Therefore, sit-ups or curl-ups only serve to increase compressive forces on the spine replicating back injury mechanics.

In an effort to protect our back during exercise, we must consider the muscles that function to protect the spine.  In particular, the transverse abdominis (TVA), a deep abdominal muscle, has received much attention with respect to spinal stability because of its orientation running horizontally around the abdomen. There are many trainers and therapists that advocate TVA activation to stabilize the spine, because research shows that together with the internal and external oblique the TVA increases intra-abdominal pressure when the abdomen is drawn inward or “hollowed,” therefore imparting functional stability of the lower back.

Abdominal Bracing Versus Hollowing

Instead, Dr. Stuart McGill, a leading spine biomechanist suggests that pulling or hollowing in the abdominals to “activate the transverse abdominis” to enhance spinal stability fails to actually stabilize the spine at all and that trainers who focus on this approach are misdirected. McGill (2009) found that abdominal hollowing techniques reduces the potential energy of the spinal column causing the spine to fail at lower applied loads.  An additional reason is that the TVA fails to target the major stabilizers of the spine like the quadratus lumborum that functions to laterally flex the back.

Maintaining a neutral or “stiff” spine during core training has been advocated as the safest and most effective approach to creating spinal stability.  In contrast to TVA activation, McGill suggests that abdominal bracing enhances spinal stability.  An abdominal brace occurs when there is simultaneous co-contraction of the abdominals, lower back, and buttock muscles.  To perform abdominal bracing, the abdominal muscles are contracted (as if getting punched in the stomach) as well as the buttocks, which should generate simultaneous contraction of the lower back muscles. Another way to feel this contraction is to cough or simulate blowing out a candle.

Enhancing Spinal Stability

With an isometric abdominal brace, McGill suggests that all three layers of the abdominal wall (internal and external obliques and transverse abdominis) are co-activated with simultaneous activation of the latissimus dorsi, quadratus lumborum, and the back extensors. Therefore, the entire abdominal wall is activated from all directions as these muscle layers bind together to enhance spinal stiffness and stability.

McGill makes the analogy of a guy-wire system as on a ship mast. Core bracing assists in keeping a wide base to the guy wires and recruits the oblique muscles to create cross-bracing support for spinal stability in all directions.  In contrast, McGill suggests that abdominal hollowing to “activate the transverse abdominis” reduces the guy wire base, consequently reducing spinal stability.  In support, multiple authors comparing the effects of abdominal hollowing to bracing have found that the hollowing maneuver does not directly enhance spinal stability, whereas abdominal bracing generates torso co-contraction, reduces lumbar displacement, and increases rectus abdominis and internal and external oblique activation.

Summary

The objective of this article is not to be definitive in the argument that abdominal bracing is superior to hollowing for enhancing spinal stability.  Certainly, there are counter arguments presented against abdominal bracing.  As well, abdominal hollowing to restore TVA activation most definitely has its place. Rather, this article serves to shed light on an alternative technique to spinal stability, while hopefully bringing more awareness to the importance of spinal stability during exercise.

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References:

1.  Juker, D., McGill, S.M., Kropf, P., and Steffen, T. (1998) Quantitative intramuscular myoelectric activity of lumbar portions of psoas and the abdominal wall during a wide variety of tasks. Medical Science Sports & Exercise. 30: 301–310.

2.  Koh, H.W., Cho, S.H., & Kim, C.Y. (2014). Comparison of the Effects of Hollowing and Bracing Exercises on Cross-sectional Areas of Abdominal Muscles in Middle-aged Women. Journal of Physical Therapy Science, 26(2), 295–299. doi:10.1589/jpts.26.295

3.  McGill, S.M. (2010). Core Training: Evidence Translating to Better Performance and Injury Prevention. Journal of Strength and Conditioning, June 32(3), 33-46.

4.  McGill, S.M. (2009). Ultimate Back Fitness and Performance (4th ed). Waterloo, Canada: Backfitpro Inc, 2009. pp. 124–125.

5.  McGill, S.M. (2007). Low Back Disorders. Evidence-Based Prevention and Rehabilitation. Human Kinetics, Champaign, Illinois.

6.  Vera-Garcia, F.J., Elvira, J. L., Brown, S.H., and McGill, S.M. (2007). Effects of abdominal stabilization maneuvers on the control of spine motion and stability against sudden trunk perturbations. Journal of Electromyography Kinesiology. Oct;17(5):556-67.

Introduction

Squatting is one of the most widely used and effective movement patterns for developing strength and muscle in the front of the legs (quadriceps).   Squatting depth is often defined as either half or full squat depth.  The half squat is defined as squatting to knee angles of 40°-45°, while the full or deep squat describes squatting at of knee angles of 80°-100°.  It has been suggested that full or deep squatting should be avoided due to increase stress on the knees, thereby exposing to higher risk of knee injury.  However, this suggestion does not take into a number of influences that work to protect the knees with increased squat depth.  This article will examine the forces applied to the knees during the half and full squat and highlight some of the mechanisms that function to protect the knees in a deep squat position.

A Look At the Evidence

Squatting Knee Stresses

When squatting to full depth, a reduction in shear forces on the knees have been demonstrated specifically to the anterior cruciate ligament (ACL), a knee ligament that prevents forward movement of the shin bone over the thigh bone (tibiofemoral translation).  Multiple authors have demonstrated that, in cadaver knees, opposing hamstring load and quadriceps load minimize shear forces on the knees by limiting tibiofemoral translation and as a result reduced tensile forces on the ACL.  Hartmann et al. (2013) published a review in Sports Medicine that examined over 164 articles published between 2011-2013 and found there are no realistic estimations of increased knee-joint forces for knee-flexion angles beyond 50° in the deep squat. Also, based on biomechanical calculations and measurements of cadaver knee joints, the highest compressive forces and stresses on the knees can actually be seen at 90°, indicating that greater stresses on the knee occur when half squatting not full squatting [4].

Protective Mechanisms

Another reason deep squatting is safe for the knees is that with increased knee flexion beyond 90°, it has been suggested that a “wrapping effect” occurs, whereby the additional contact between the quadriceps (thigh muscle) tendon and the intercondylar notch (the groove between the two rounded ends of the thighbone) contributes to an enhanced load distribution and force transfer.  Therefore, a lower risk of injury in the deep squat position can be expected.

Also, the influence of soft tissue contact between the back of the thigh and the calf muscle plays a significant role in reducing the knee-joint forces beyond 40° of knee extension. During the deep squat  the back of the legs (hamstrings) come into contact with the back of the shin (calves).  This soft tissue contact has been shown to reduce tibiofemoral and patellofemoral joint forces in deep squatting range.

Furthermore, the adaptation potential of ligaments is well established from training studies.  For example, training has been shown to increase tensile strength and enhance stiffness and elasticity of the ACL knee ligament. Grzelak et al. (2012) demonstrated significantly larger ACL cross-sectional area of young weightlifters compared with age matched controls [3]. The cross-sectional area of the ACL and posterior collateral ligament (PCL) of these weightlifters were found to be 50% and 61.49% larger than those of the cadaver studies.  Given this, continual squatting at depth would gradually increase the tensile strength, and hence lower risk of injury of these knee structures [3].

Drawing Comparisons

Finally, if one argues that knee problems occur in those populations who frequently perform deep squats, it could be reasonable to suggest that international weightlifting athletes are predisposed to a high prevalence of acute and chronic knee injuries with long training interruptions.

However, Calhoon et al. (1999) studied 27 weightlifters from different US Olympic training centres and showed that only 3.3 injuries occurred per 1000 training hours over a 6-year period. Of missed training time due to knee problems, 95.3 % lasted 1 day or less, and in the remaining cases, lasted less than 1 week [2].  Also, these training interruptions were primarily related to tendinitis due to chronic overuse and in very few cases to muscle strains due to acute injuries [2].  These findings were echoed by Lavallee et al. (2010) in a 4-year retrospective study that found of 1,109 weightlifters (age 12–20 years) that participated in national or international competitions, zero showed any injuries (i.e. at the knee joints) that required surgery or hospitalisation [5].

Conclusions

There is sufficient evidence to suggest that a number of mechanisms function to protect the knees during increased squat depth.  Even when examining knee injuries among international weightlifting populations, who clearly squat at depth, there is no evidence of training absences due to knee related injuries.   Furthermore, from an anatomical perspective, normal range of movement for the knee joint is 110 – 130 degrees of flexion.  Given this, it is also reasonable to suggest that squatting below 90 degrees of knee flexion adds functional value.

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References:

1.  Cabaud HE, Chatty A, Gildengorin V, et al. Exercise effects on the strength of the rat anterior cruciate ligament. Am J Sports Med. 1980;8:79–86.

2,  Calhoon G, Fry AC. Injury rates and profiles of elite competitive weightlifters. J Athl Train. 1999;34:232–8.

3.  Grzelak P, Podgorski M, Stefanczyk L, et al. Hypertrophied cruciate ligament in high performance weightlifters observed in magnetic resonance imaging. Int Orthop. 2012;36:1715–9.

4.  Hartmann H, Wirth K, Klusemann M. Analysis of the Load on the Knee Joint and Vertebral Column with Changes in Squatting Depth and Weight Load. Sports Med. 2013;43:993-1008.

5.  Lavallee ME, Balam T. An overview of strength training injuries: acute and chronic. Curr Sports Med Rep. 2010;9:307–13.

6.  Noyes RF, Grood ES. The strength of the anterior cruciate ligament in humans and rhesus monkeys. J Bone Joint Surg. 1976;58-A:1074–82.

7.  Race A, Amis AA. The mechanical properties of the two bundles of the human posterior cruciate ligament. J Biomech. 1994;27:13–24.

Muscle growth, more formally known as muscle hypertrophy, is a primary goal within exercise.  Lean muscle mass helps to create the appearance of a toned and defined physique in addition to contributing to enhanced muscular strength.  When working with a personal trainer on weight lifting, the overload stimulus caused by resistance leads to disruptions in the muscle fibers and extracellular matrix [7].  Muscle fibers are the cells or basic building blocks of muscle and the extracellular matrix can be thought of as the physical scaffolding of muscle [7].

Mechanical Tension

It is theorised that resistance exercise creates tension on muscle and disrupts its structural integrity [7].  During resistance exercise, there is greater force production and stretch on the muscle which causes mechanical and chemical changes on a molecular and cellular level.  These changes lead to an increased rate of muscle protein synthesis, which is the building of new muscle proteins, essential for muscle growth [7].

On a cellular level, mechanical tension contributes an important cell signaling process involving a protein called mammalian target of rapamycin or mTOR [1, 7].  This specific protein is highly important to muscle hypertrophy because there is a direct relationship between mTOR and muscle protein synthesis [1].  Increased mechanical tension during resistance exercise by way of lifting heavier weights, enhances mTOR activation resulting in more muscle growth [1].

Passive tension, which is created during the eccentric, or lengthening phase of a lift, helps to further increase the active tension on a muscle or the contraction phase of a lift, which enhances the hypertrophic response [7].  Importantly, mechanical tension is directly related to intensity, defined as load or amount of resistance applied.  The greater the load applied during resistance exercise, the greater the mechanical tension placed on the muscle.  

3 Factors Influencing Muscle Growth

Muscle Damage

It is well established that resistance exercise can lead to localised muscle tissue damage [7].  A previous blog post examined the causes of delayed onset muscle soreness (DOMS) and identified microtears to the connective tissue, contractile elements of muscle and surrounding structures as a primary cause of DOMS.  This damage to muscle results in an acute inflammatory response [7].  During this inflammatory phase, neutrophils, macrophages and lymphocytes, all types of white blood cells that help fight infection, migrate to the damage site to clean unwanted debris [7].  The release of these white blood cells along with other cells are believed to result in the release of growth factors that regulate the rapid increase of highly important healing cells known as satellite cells [7]. 

Satellite cells are the equivalent of stem cells, but in the muscle [6].  They are considered the limiting factor in muscle development and increasing their activity stimulates more muscle growth [6].  Satellite cells are located close to a muscle fiber and remain inactive unless awoken by strenuous exercise [6].  Once awoken by exercise, these cells multiply and bind to existing muscle fibers to supply the precursors required for repair and growth of new muscle tissue [6].  Therefore, muscle damage, up to a certain level, can promote increased activation of satellite cells and ultimately muscle hypertrophy.  

Metabolic Stress

The hypertrophy effects of metabolic stress are attributed to the production of metabolic byproducts in the blood during strenuous exercise called metabolites [6].  These metabolites include lactate, hydrogen ion, inorganic phosphate, creatine and others [6, 7].  It theorised that this build up of metabolites are achieved by increasing water within muscle, a phenomenon known as cell swelling [6].  There is evidence suggesting cell swelling increasing muscle protein synthesis while simultaneously decreasing protein breakdown, creating an anabolic effect conducive to muscle growth [6].  

It is hypothesised that cell swelling occurs as a self-preservation mechanism [6].  Analogous to over-inflating a rubber tire, increasing water in muscle cells exerts pressure agains the cell wall [6]. This pressure is likely perceived as a threat to muscle integrity and the anabolic response is initiated to strengthen muscle structure [6].  

The hypertrophic effects of metabolic stress can be found in Kaatsu training studies, where resistance training is combined with blood flow restriction [5].  Kaatsu training utilises low intensities (generally <40% 1-repetition maximum), while using a blood pressure cuff to induce muscle ischaemia (reduced blood flow to muscle) [5].  A number of studies show this method of training produces an anabolic effect, muscle protein synthesis and leads to marked increased in muscle hypertrophy [3, 4].

Summary

The processes responsible for muscle hypertrophy are complex and not well understood.  However, it is suggested that mechanical tension, muscle damage and metabolic stress are primary mechanisms contributing to muscle development [6].  Although each mechanism exhibit different physiological effects, they do not act independently, but rather work in concert to produce anabolic effects for muscle hypertrophy [6].  Importantly, only an optimal combination of training variables within a resistance training program can maximise the anabolic effects of each mechanism.  A well organised resistance program that manipulates intensity (load) and volume (repetitions and sets) are essential for encouraging muscle growth.

References:

1. Drummond, M. J. et al. 2009. Nutritional and contractile regulation of human skeletal muscle protein synthesis and mTORC1 signaling. Journal of Applied Physiology. April. Vol.106, No. 4, pp.1374-84.

2. Frantz, C. et al. 2010. The extracellular matrix at a glance. Journal of Cell Science. December. Vol.123(Pt 24), pp.4195-200.

3. Fry, C. S. et al. 201. Blood flow restriction exercise stimulates mTORC1 signaling and muscle protein synthesis in older men. Journal of Applied Physiology. May. Vol. 108, No. 5, pp.1199–209.

4. Loenneke, J. P. et al. 2012. Low intensity blood flow restriction training: a meta-analysis. European Journal of Applied Physiology. May. Vol. 112, No. 5, pp.1849–59.

5. Schoenfeld, B. J. 2013. Potential Mechanisms for a Role of Metabolic Stress in Hypertrophic Adaptations to Resistance Training. Sports Medicine. March. Vol. 43, No. 3, pp.179-194.

6. Schoenfeld, B. J. 2013. The Max Muscle Plan. Human Kinetics: Champaign, IL.

7. Schoenfeld, B. J. 2010. The mechanisms of muscle hypertrophy and their application to resistance training. Journal of Strength and Conditioning Research. October. Vol. 24, No. 10, pp.2857-72.

What is a Rest Interval?

Rest intervals can be defined as the total period of rest or relief between sets during exercise [4].

A Brief Overview

In resistance training, whether the goal is to increase muscle mass (hypertrophy) or strength, the rate at which muscular adaptation occurs is dependent on specific training variables (i.e. repetitions, sets, load, rest intervals) [11].  Volume (repetitions and sets) and load (amount of resistance) receive the greatest attention in resistance training because they remain the greatest drivers of strength and muscle hypertrophy [11].  However, the correct manipulation of rest intervals can play an important role in maximising muscle growth, strength, endurance or power.

Rest intervals are typically prescribed according to the client’s goal (e.g. strength, hypertrophy, power or endurance) [4].  Presently, guidelines from The American College of Sports Medicine recommend rest intervals between 1-2 minutes for novice and intermediate lifters wanting to build muscle and longer rest intervals of 2-3 minutes for advanced lifters using heavier loads [9]. Some authors advocate even shorter rest intervals of 30-60 seconds to generate muscle hypertrophy gains, while using longer rest intervals of 3 minutes or more to maximise strength gains [4].

General recommendations for short rest intervals of 30-60 seconds are based on research that shows acute elevations in anabolic hormones, namely growth hormone [9].  A number of studies indicate that increases in growth hormone act as an anabolic signal to increase muscle mass and enhance muscular adaptation [10].

A Look Into the Research 

Rest Intervals to Maximise Strength

Few studies examine the effects of varying rest intervals on muscular strength and the available literature conflict in their findings.

A literature review by de Salle and colleagues (2009) examined 35 studies to determine the effects of rest intervals on the acute and chronic muscular adaptations to resistance exercise [4].  With respect to strength improvement, rest intervals between 3-5 minutes were found to produce greater long-term absolute strength gains [4].  Findings from this review showed that when using loads between 50-90% of 1-repetition maximum (RM), a rest interval between 3-5 minutes between sets allowed for more volume to be performed (more repetitions and sets) [4]

In support, Shoenfeld and colleagues (2015) found that longer rest intervals (3 minutes) produced greater strength gains than shorter rest intervals (1 minute) following 8-weeks of resistance training with 3 total body workouts each week [11].

Since it is well established that shortening rest reduces the number of repetitions performed, longer rest periods may allow for a greater volume of work through higher repetitions in addition to greater training intensity (higher load), which may contribute to enhanced strength gains [9, 11].

However, findings from two studies investigating the effects of different rest periods on strength run contrary to the above findings. In both studies, employing a longer rest interval (4 or 5 minute) was either less, or no more, effective than using a shorter rest interval (1 or 2 minute) to elicit strength gains [2, 12].

Rest Intervals to Maximise Hypertrophy

In the literature review by de Salle and colleagues (2009), their assessment found that shorter rest intervals of 30-60 seconds between sets of moderate-intensity proved most effective for goals of muscle hypertrophy [4].  The authors suggest that shorter rest periods produce a greater hypertrophic effect because it results in higher increases in acute growth hormone [4].

However, despite some evidence showing acute increases in growth hormone levels with rest intervals less than 1-minute, the available evidence is highly conflicting [9].  A study by Kraemer and colleagues found that shorter rest intervals (1-minute) did increase acute levels of growth hormone in young men and women.  However, increases in cortisol were simultaneously found, which counteract the anabolic effects of growth hormone.  Therefore, the acute increases in growth hormone may not reflect long-term muscle hypertrophic gain.  Furthermore, a study by Ahtiainen and colleagues (2005) showed that both short (2 minute) and long (5 minute) rest periods resulted in the same acute increases in growth hormone concentrations immediate following a workout [12].

A second, recent (2014), literature view by Henselmans and Shoenfeld was conducted to understand the effects of manipulating rest intervals to enhance specifically muscular hypertrophy [9].  In their review, enhanced muscle hypertrophy was evidenced by increases in muscle cross sectional area (MCSA).  An examination of studies measuring long-term muscle hypertrophy revealed that longer intervals (2.5-5 minutes) were more effective than shorter rest intervals (1-2 minutes) for enhancing muscle hypertrophy [9].  The authors of this review suggest that longer rest intervals may enhance muscle hypertrophy because it allows for higher training loads to be used compared to shorter rest intervals [9].  For example, Buresh and colleagues (2009) showed that a 2.5-minute rest period allowed for significantly greater training loads to be used when compared against the 1-minute rest interval group and this increase in work volume may have contributed to enhanced muscle hypertrophy [3].

Additional support that shorter rest intervals do not contribute to greater muscle hypertrophy was demonstrated by De Souza et al. (2010) [5].  In this study, twenty young, recreationally trained men were randomly assigned to either a constant rest group (2-minutes) or decreasing rest group (2-minutes decreasing to 30-seconds) [5].  Both groups performed 8-weeks of resistance training using the same volume (2 weeks of 3 sets x 10-12RM, then 6 weeks of 4 sets x 8-10RM) [5]. The findings from this study showed that short or descending rest intervals were equally as effective as longer intervals for eliciting muscle hypertrophy gains [5].

Recently (2015), Shoenfeld and colleagues investigated whether short or long rest periods led to greater hypertrophy gains in young, resistance-trained men [11].  In this study, subjects were randomly allocated to either resistance training with 1-minute rest intervals (SHORT) or 3-minute rest intervals (LONG) [11].  The subjects performed 8-weeks of training involving 3 total body workouts each week comprised of 3 sets of 8-12RM [11].  Ultrasound imaging, considered the gold standard for measuring muscle growth, was used to assess hypertrophy gains.

The above study found muscle growth was greater in the thigh, triceps and biceps for LONG rest intervals compared to SHORT [11].  In theorising why longer rest periods led to increased hypertrophic gains, the authors of this study suggest that longer rest periods allowed for greater training loads to be used [11].  This hypothesis is supported by the previously mentioned study by Buresh and colleagues (2009) that found greater hypertrophic gains corresponded with significantly greater training loads [3].

Noteworthy, one study by Ahtiainen and colleagues (2005) found that neither a shorter (2 minute) or longer (5 minute) rest interval had any difference in enhancing hypertrophic gains among young, trained men [12].  Also, Villeneuva and colleagues (2015) found that short rest periods (60 seconds) were more effective than longer rest intervals (4 minutes) for improving strength gains over an 8-week period of resistance training [12].

Rest Intervals to Maximise Endurance

Muscle endurance can be defined as “the capacity to sustain submaximal muscle actions for an extended period of time” [4].

The literature review by de Salle and colleagues (2009) revealed that rest intervals of 20 seconds to 1 minute were best for improving muscular endurance [4].  Among the included studies, Hill-Haas and colleagues (2007) examined the effect of altering rest intervals on adaptations to high-repetition resistance. [8].  In their study, 18 active females were randomly allocated to a resistance-training group with either short (20 seconds) or long rest periods (80 seconds) [8].  Each group trained 3 times a week for 5 weeks and performed repeated sprint cycling (5 x 6-second max cycle sprints) in addition to an upper and lower body resistance-training program [8].  Participants completed 15-20 repetitions for 2-5 sets on each resistance exercise [8].  At the end of the 5 weeks of training, the short rest group produced greater improvements in repeated-sprint performance than the long rest group [8].  This study suggests that shorter rest used with higher repetitions (15-20 reps) can improve sprint-cycle endurance more than longer rest periods and may have applications to prescribing rest intervals for resistance training specific to endurance goals.

However, Shoenfeld and colleagues (2015) found no significant difference in short  (1 minute) and long rest periods (3 minute) on muscle endurance.   In their study, muscle endurance was assessed by having subjects perform the bench press at 50% of their 1RM until muscular failure. Similarly, Garcia and colleagues (2007) found no differences in muscular endurance gains with either short  (1 minute) or long rest periods (4 minute) after 5 weeks of elbow-flexion resistance exercise at 60% of 1RM [6].

Rest Intervals to Maximise Power

In their assessment of rest interval length on acute expression of power, de Salle and colleagues (2009) suggest that 3-5 minutes rest intervals were found to elicit greater muscle power when compared to shorter rest intervals of 1 minute [4]. As power is highly reliant on anaerobic energy metabolism, specifically the replenishment of phosphocreatine (PCr), rest intervals should be sufficient enough to allow for replenishment of PCr [4].

In the body, PCr is broken down to supply adenosine triphosphate (ATP), which provides immediate energy for short duration, maximal intensity exercise for up to approximately 12 seconds [7]. If rest intervals are insufficient for PCr replenishment, energy production then shifts to use the glycolytic system [4,7].  The glycolytic system is not as efficient for producing power compared to the ATP system and is better suited to exercise lasting from 30 seconds to 2 minutes [7].

A study by Abdessemed and colleagues (1999) investigated the effects of rest intervals on power and blood lactate levels.  In their study, 10 males performed 10 sets of 6 repetitions of bench press at 70% of 1RM using 1, 3 or 5 min rest intervals [1].  This study found that short rest periods of 1 minute resulted in a significant decrease in muscular power compared to longer rest periods of 3 and 5 minutes [1]. The fatigue experienced by subjects using 1 minute rest intervals was attributed to insufficient time for PCr replenishment [1].  Therefore, resting 3 minutes or more between sets may be required to enhance muscular power.

Conclusions

Manipulating resistance training variables (sets, repetitions, load) to maximise muscular adaptations is well understood.  Yet, few personal trainers consider the science behind manipulating rest intervals specific to a clients training goal.  A scarcity of evidence is presently available to make definitive recommendations for rest intervals directed to maximise strength, hypertrophy, endurance or power goals.  However, based on the available evidence, it appears that rest intervals of 3 minutes would be optimal for maximising muscular strength.  For maximising hypertrophic response, rest intervals of 2 minutes would allow for greater training loads to be used compared to those that favour shorter rest intervals (30-60 seconds).  There is more conflicting evidence when considering optimal rest intervals to maximise muscular endurance.  Shorter rest interval of 60 seconds or less may prove beneficial for optimising for endurance, although more research is required to understand this particular area.  Finally, rest intervals of 3-5 minutes would allow for sufficient PCr replenishment and appear to be optimal for maximising muscular power.

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References

1. Abdessemed, D. et al. 2009. Effect of recovery duration on muscular power and blood lactate during the bench press exercise. International Journal of Sports Medicine. August. Vol. 20, No. 6, pp. 368-373.

2. Ahtiainen, J.P. et al. 2005. Short vs. long rest period between the sets in hypertrophic resistance training: influence on muscle strength, size, and hormonal adaptations in trained men. Journal of Strength and Conditioning Research. August. Vol. 19, No. 3. pp. 572-582.

3. Buresh, R. et al. 2009. The Effect of Resistance Exercise Rest Interval on Hormonal Response, Strength, and Hypertrophy with Training. Journal of Strength and Conditioning Research. January. Vol. 23, No. 1, pp.62-71.

4. de Salles, B. F. et al. 2009. Rest Interval between Sets in Strength Training. Sports Medicine. Vol. 39, No. 9, pp. 765-777.

5. de Souza, T.P. Jr. et al. 2010. Comparison between constant and decreasing rest intervals: influence on maximal strength and hypertrophy. Journal of Strength and Conditioning Research. July. Vol. 27, No. 7, pp.1843-1850.

6. Garcia-Lopez, D. et al. 2007. Effects of short vs. long rest period between sets on elbow-flexor muscular endurance during resistance training to failure. Journal of Strength and Conditioning Research. November. Vol. 21, No. 4, pp.1320-1324.

7. Greenhaff, P. L. 2001. The creatine-phosphocreatine system: there’s more than one song in its repertoire. Journal of Physiology. December. Vol. 15, pp. 537 (PT.3). p.657.

8. Hill-Haas et al. 2007. Effects of rest interval during high-repetition resistance training on strength, aerobic fitness, and repeated-sprint ability. Journal of Sports Sciences. April. Vol. 25, No. 6, pp. 619-628.

9. Henselmans, M. and Shoenfeld, B. J. 2014. The Effect of Inter-Set Rest Intervals on Resistance Exercise- Induced Muscle Hypertrophy. Sports Medicine. December. Vol. 44, No. 12, pp. 1635-1643.

10. Rennie, M. 2003. Claims for the anabolic effects of growth hormone: a case of the Emperor’s new clothes? British Journal of Sports Medicine. April. Vol. 37, No. 2, pp. 100-105.

11. Shoenfeld, B. J. et al. 2015. Longer inter-set rest periods enhance muscle strength and hypertrophy in resistance trained men. Journal of Strength and Conditioning Research. November.

12. Villanueva, M. G. et al. 2015. Short rest interval lengths between sets optimally enhance body composition and performance with 8 weeks of strength resistance training in older men. European Journal of Applied Physiology. February. Vol. 115, No. 2. pp. 295-308.

What Is Delayed Onset Muscle Soreness?

Delayed onset muscle soreness (DOMS) is a familiar feeling for most lifters.  It is a distinct feeling of discomfort in the working muscle that can range symptomatically from simple muscle tenderness to severely debilitating pain [3, 11].  What is interesting about exercise induced muscle soreness is that it typically increases in discomfort and begins with a generally pain-free period of about 24 hours after strenuous exercise [4, 11].  Pain symptoms then increase rapidly and typically peak at 24-72 hours following a workout and dissipate within 5-7 days following exercise [1, 2, 4, 11].

DOMS can be formally classified as a type I muscle strain injury and is the result of eccentric (lengthening) type of a movement like the lowering of free weights or running downhill.  This movement is in contrast to the shortening (concentric) type of the movement [11, 6].  There have been a number of theories presented to explain DOMS.  This blog post will examine the more popular theories in an effort develop a better understanding of the mechanisms behind this phenomenon.

Lactic Acid Theory

Most common among the general lifting population is the assumption that DOMS occurs from the accumulation of lactic acid.  Lactic acid is a compound produced mainly in muscle cells and forms when the body breaks down carbohydrates under low oxygen levels (i.e. strenuous exercise or infection) [14].  The build up of metabolic waste in the form of lactic acid is thought to cause painful stimulation and the perception of pain at a delayed point [1, 6, 11, 14].  However, this theory has been widely rejected as lactic acid levels have been shown to return to pre-workout levels within 1 hour following strenuous exercise [3, 14]. Also, this hypothesis is negated by findings that show concentric (shortening) exercise, which involves a higher degree of metabolism, fails to elicit DOMS [5].  Therefore, lactic acid may explain the acute pain or soreness following intensive exercise, but it is not attributed to the delayed pain experienced 24-48 hours post exercise.

Muscle Spasm Theory

Many lifters have likely experienced involuntary muscle activity (spasming) following an intensive workout.  It was theorised that increased resting muscle activity following eccentric exercise led to compression of local blood vessels, ischemia (inadequate blood supply to the muscles) and a build up of pain substances [2].  These factors were then thought to stimulate pain nerve endings and cause further muscle spasms, creating somewhat of a pain evoking cycle [2].  However, studies examining muscle spasms using electromyography (EMG) have been largely inconsistent with multiple studies showing no relationship with increased EMG activity and the perception of sore muscles [2].

Muscle Damage Theory

The muscle damage theory was first proposed by Hough in 1902 and remains one of the strongest explanations of DOMS [8].  This theory focuses on the mechanical damage to connective muscle tissue following strenuous eccentric exercise.  Eccentric exercise places increased tension on the muscles creating microscopic lesions (small tares) in the muscle itself, specifically damaging the z-lines and muscle sarcomeres [1, 3, 4, 10].  During eccentric exercise, the force generated is approximately twice that developed during isometric exercise [8, 6].  Pain receptors located within the muscle connective tissue are then stimulated resulting in the sensation of pain [3].

Newham and colleagues (1983), found immediate muscle damage in the quadriceps muscle following eccentric exercise [12].  In their study, subjects performed a 20-minute step test, whereby the quadriceps muscle of one leg contracted concentrically throughout by stepping up, while the quadriceps muscle of the opposite leg contracted eccentrically by controlling the step down [12].  This study found marked muscle damage in the eccentrically controlled leg 24-48 hours post-exercise, while no muscle damage was found in the concentrically exercised leg [12].  The authors suggest that the initial muscle damage observed in the eccentrically exercised leg was related to mechanical damage to the connective tissue, reinforcing Hough’s muscle damage theory.

It is purposed that increased muscle tension alone is not the only cause of muscle damage, but rather the strain during active lengthening.  Liber and Friden suggest the active strain of a muscle during eccentric lengthening exceeds that of the structure or framework of a muscle, therefore imparting muscle damage [9].

In further support of the muscle damage theory, creatine kinase (CK), a blood enzyme found exclusively in cardiac and skeletal muscle, rises significantly following eccentric exercise [2, 3].  CK is considered a reliable indicator of muscle membrane permeability and damage to the muscle from intensive exercise would enable diffusion of soluble muscle enzymes, like CK, into the interstitial fluid [2, 3].  In 1983, Newham and colleagues showed that CK levels increased from 400 IU/liter up to 34,500 IU/liter following exercise delivered in the form of an eccentric 20-minute step-test, indicating a strong connection between muscle damage and delayed muscle soreness [13].

Inflammation Theory

The inflammation theory is based on findings of an inflammatory response i.e. oedema (swelling) and cell infiltration following strenuous eccentric exercise.  Following eccentric exercise, there is a rapid breakdown of muscle fibres and connective tissue and an accumulation of inflammatory mediators (bradykinin, prostaglandins and histamine) to the damaged site [7].  This is accompanied by an increase in protein-rich fluid (swelling) into the muscle following exercise [5].  The sensation of pain results from the increased fluid pressure (osmotic pressure) activating pain sensory neurons within the muscle [1, 3, 5, 15].  Also, peak swelling periods appear to coincide well with heightened levels of muscle soreness.

Furthermore, it has been argued that following eccentric exercise, monocytes and macrophages, which are defence cells, responsible for removal of waste from the damaged muscle, accumulate at the injured site and sensitise nerve endings around 24-48 hours post exercise [1, 15].  However, there is still controversy in the scientific literature as to whether swelling (oedema) and inflammatory cell infiltration is purely responsible for delayed muscle soreness post exercise.

Conclusions

As personal trainers, understanding the possible mechanisms behind DOMS is vital for client education and the circulation of evidence-based education.  A review of the literature suggests that more than one theory alone can be used to explain the onset of DOMS.  However, it can be safely argued that the process begins with application of high tensile muscle forces associated with eccentric exercise, which damage the muscle and connective tissue [3].  This is evidenced by damaged z-lines in the muscle and increased levels of the blood enzyme creatine kinase.  This stage is immediately followed by swelling and inflammatory cell infiltration within the first few hours, which peak at about 48 hours post exercise.  The sensation of pain is then a result of damage to the muscle itself and an exposure to the inflammatory environment that further sensitises pain nerve endings.

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References:

1.  Armstrong, R.B. 1984. Mechanisms of Exercise-Induced Delayed Onset Muscular Soreness: A Brief Review. Medicine and Science in Sports and Exercise. December. Vol. 16, No. 6, pp. 529–538.

2.  Bobbert, M. F, et al. 1986. Factors in Delayed Onset Muscular Soreness of Man. Medicine and Science in Sports Exercise. February. Vol. 18 , No. 1, pp. 75-81.

3.  Cheung, K. et al. 2003. Delayed Onset Muscle Soreness Treatment Strategies and Performance Factors. Sports Medicine. Vol. 33, No. 2, pp. 145-164.

4.  Faulkner J. A. et al. 1993. Injury to skeletal muscle fibers during contractions: conditions of occurrence and prevention. Physical Therapy. December. Vol. 73, No. 12, pp. 911-921.

5.  Friden, J. et al. 1986. Muscle soreness and intramuscular fluid pressure: comparison between eccentric and concentric load. Journal of Applied Physiology. December. Vol. 61, No. 6, pp. 2175-2179.

6.  Gulick, D. T. & Kimura, I. F. 1996. Delayed Onset Muscle Soreness: What is it and How Do We Treat It? Journal of Sport Rehabilitation. August. Vol. 5, No. 3, pp. 234-243.

7.  Hasson, S. M. et al. 1993. Effect of ibuprofen use on muscle soreness, damage, and performance: a preliminary investigation. Medicine & Science in Sports Exercise. January. Vol. 25, No. 1, pp. 9-17.

8.  Hough, T. 1902. Ergographic Studies in Muscular Soreness. American Jouranl of Physiology. April. Vol. 7, pp. 76–92.

9.  Lieber, R. L. & Friden. 1993. Muscle damage is not a function of muscle force but active muscle strain. Journal of Applied Physiology. February. Vol. 74, No. 2, pp. 520-526.

10.  MacIntyre, D. L. et al. 1995. Delayed muscle soreness. The inflammatory response to muscle injury and its clinical implications. Sports Medicine. July. Vol. 20, No. 1, pp. 24-40.

11.  Mizumura, K. & Taguchi, T. 2016. Delayed onset muscle soreness: Involvement of neurotrophic factors. The Journal of Physiological Sciences. January. Vol. 66, No. 1, pp. 43-52.

12.  Newham et al. 1983. Large Delayed Plasma Creatine Kinase Changes After Stepping Exercise. Muscle & Nerve. June. Vol. 6, No. 5, pp. 380-385.

13.  Newham et al. 1983. Ultrastructural changes after concentric and eccentric contractions of human muscle. Journal of the Neurological Sciences. September. Vol. 61, No. 1, pp. 109-122.

14.  Schwane, J. A. et al. 1983. Is Lactic Acid Related to Delayed-Onset Muscle Soreness? The Physician and Sportsmedicine. January. Vol. 11, No. 3, pp.124–131.

15.  Smith, L. L. 1991. Acute inflammation: the underlying mechanism in delayed onset muscle soreness? Medicine & Science in Sports Exercise. May Vol. 23, No. 5, pp. 542-551.

Introduction

Daily undulating periodisation (DUP) and linear periodisation (LP) are both concepts that are based upon the last two decades of exercise science research.  DUP is a newer concept that manipulates training variables with greater frequency to maximise improvements in muscular strength, hypertrophy or athletic performance.

The purpose of all exercise is to apply stress to the body and interrupt homeostasis. which is the optimal internal environment the body functions under [8]. This occurs because the body views exercise as a threat to its survival and results in deviation from optimal homeostatic functioning. As a result, when we apply stress from exercise, the body undergoes an adaptive response to better cope with the stimulus in the future [8].

In 1936 Hans Selye developed a stress Theory of General Adaptation Syndrome (GAS) that explains how, under exercise stimulus, the body responds with a temporary decrease in performance followed by a return to, or above, the initial level of fitness [9]. This adaptation is called supercompensation and the primary explanation for why physical fitness levels improve from consistent exercise [9]. Importantly, if the exercise stimulus applied to the body remains unchanged from its initial magnitude (volume, intensity, frequency), the body accommodates to the stress and no additional improvements occur. [9].

To prevent accommodation, exercise programs need to be varied over time. Given this, the application of periodisation has become increasingly relevant to improving physical fitness and performance. Periodisation refers to the systematic structuring and planning of training variables (volume, intensity, frequency, rest) throughout specified time periods with the aim to maximise performance and minimise overtraining and accommodation [1, 2, 10]. There are two primary forms of periodisation: linear periodisation (LP) and undulating periodisation (UP), also called non-linear periodisation (NLP) [10].

Linear Periodisation (LP)

Linear periodisation is typically divided into three components:

1. Microcycle   –  A period of days or weeks
2. Mesocycle    –  A period of serval weeks or months
3. Macrocycle  –  A period of several months to four years

A characteristic of LP is the progression of starting with high volume (repetitions and sets) and low intensity (load) and progressing gradually in intensity while decreasing in volume [2]. Provided below is an example of LP for a five-month macrocycle. In this example, the repetitions are relatively high at the beginning of the program in weeks 1-4 and intensity levels are lower. However, these variables are reversed towards the end of the program as the amount of weight lifting increases and the number of repetitions decreases.

Repetition maximum describes the amount of weight lifted (intensity) and a one-repetition maximum (1RM) refers to the maximal amount of weight lifted for one repetition [8]. For example, if the maximal amount of weight lifting for one repetition in a bench press is 50kg, then 50% of 1RM for this exercise would be 25kg.

Undulating Periodisation (UP)

Undulating periodisation involves more frequent (days, weeks, bi-weekly) variation in training variables [2]. UP is commonly integrated as daily undulating periodisation (DUP) or weekly undulating periodisation (WUP), whereby volume and intensity is manipulated over the period of either days or weeks [10].

Provided below is an example of DUP model for an individual that performs resistance exercise three days a week over a 4-week mesocycle. The final week incorporates a de-load week that uses lower intensities and volumes and functions as a period of recovery to prevent overtraining.  In the DUP example, volume (repetitions and sets) and intensity (percentage of 1RM) changes each training day. Also, at the start of each new week, intensity is altered again increasing from the previous week.

Provided below is an example of WUP for an individual that performs resistance exercise three days a week over the same 4-week mesocycle.  In the WUP example, volume and intensity are maintained for a week (microcycle), then altered the subsequent week.  It is not required that variables be changed to follow a set pattern as there a infinite methods to integrate undulating periodisation models.  In the below example, a week incorporating lighter intensity is interjected between week 1 and 3.

Is Daily Undulating Periodisation Best for Strength Improvement?

Multiple studies have examined undulating versus linear periodisation for strength improvements and lean muscle enhancement.  The earliest application of undulating periodisation can be found with the intensification and accumulation phases proposed by Poliquin (1988) [5].  For increasing strength, Poliquin first proposed short periodic integration of accumulation phases composed of higher volume and lower intensity with intensification phases of lower volume and higher intensity [5].

The concept of undulating periodisation is that training variables (volume, intensity) are altered more frequently than in linear periodisation thereby enhancing neuromuscular stimulation [10].  Within undulating periodisation models that alter variables every two weeks, Poliquin identified no apparent benefit to strength gains compared to linear periodisation [5].  However, with more frequent changes in training variables, as within daily undulating periodisation, the muscles do not accommodate to the exercise stimulus, therefore permitting a higher response to training [10].

Since Poliquin’s proposed theory, a number of studies have evaluated DUP against LP for strength gains.  A classic study by Rhea and colleagues (2002) compared LP and DUP for strength improvements among resistance trained men [6].  In their study, the authors randomly allocated twenty men with about five years of training experience to ether a LP or DUP group [6].  One repetition maximum was tested for both the leg press and bench press [6].  Each group trained three days per week for twelve weeks.  Training protocols for each group consisted of the following [6]:

Both groups performed the same amount of training, however the DUP group ordered their training with shorter undulation in volume and intensity [6].  Interestingly, compared with the LP group, the DUP group experienced almost twice the improvement within the bench press 28.8% versus 14.4% and leg press 55.8% versus 25.7% [6].

A potential limitation within this study were that subjects within the LP group were stronger prior to commencing study possibly leaving greater room for strength improvement.

A similar, more recent study by Miranda and colleagues (2011) compared DUP with LP at 1RM and 8RM loads in the bench press and leg press [4].  Twenty recreationally trained men were randomly allocated to either LP or DUP and performed four weekly training sessions alternating upper and lower body sessions as follows [4]:

Although both groups performed a number of supplementary exercises, only the bench press and leg press were periodised [4].  For all assistance exercises, 3 sets of 6-8RM was applied [4].  Following 12-weeks, both the LP and DUP groups showed improvement in the bench press at 1RM loads (15% and 16% respectively) and at 8RM loads (18% and 19% respectively) [4].

In the leg press, both groups similarly improved at 1RM loads (10% and 18% respectively) and at 8RM loads (17% and 23% respectively) [4].  Although no statistical significance was found between groups, the DUP group demonstrated a greater effect size (ES) in 1RM and 8RM loads for both bench press and leg press compared with the LP group [4].

Is Daily Undulating Periodisation Best for Muscle Development?

While there is evidence to suggest that DUP may elicit greater strength improvements compared to LP, there is less available literature comparing different periodisation models on muscle hypertrophy (muscle development).  Schoenfeld and colleagues (2015) performed a study that randomly allocated 19 resistance trained men to two groups: VARIED routine and CONSTANT routine group [7].  For each group, the following resistance training protocol was used:

The authors of this study used ultrasound imaging to measure muscle cross sectional areas as a determinant of muscle growth [7].  Results showed that both VARIED and CONSTANT groups greatly improved in measures of muscle thickness for the elbow flexors (6.6% and 5.0%), elbow extensors (6.4% and 4.2%), and quadriceps (7.6% and 8.6%) [7].  Although no statistically significant between group differences were found, effect sizes favoured the VARIED group over CONSTANT group for elbow flexor thickness (0.72 versus 0.57) and elbow extensor thickness (0.77 versus 0.48), suggesting a possible benefit to daily undulating periodisation [7].

Notable limitations in the Schoenfeld study include muscle thickness measurement occurring only at the mid-point of each muscle and not at distal or proximal ends, which may have revealed differential growth changes [7].  Also, there were potential dietary compliance issues among subjects despite a dietary regimen [7].  Finally, failure to perform muscle biopsy may exclude the possibility of fibre-type specific adaptations [7].

In another study, Kraemer and colleagues (2003) examined the effects of varied versus constant condition loading over 9-months [3].  In their study, 30 women collegiate tennis athletes performed whole body resistance training 3-days per week using either a constant protocol (3 x 8-10RM) or varied protocol (4–6RM on Day 1, 8–10RM on Day 2, 12–15RM on Day 3) [3].  The authors used a 3-site skin fold measurement to assess body composition changes [3].  Results from this study showed significantly greater changes in fat-free mass in the varied group compared with constant group (3.3 ± 1.7 kg versus 1.6 ± 2.4 kg) [3].

Summary

Different to linear periodisation, undulating periodisation allows for variable loading through a selected period, which may prove advantageous for neuromuscular stimulation compared to a linear model.  With more frequent alterations in training variables (volume, intensity, frequency), daily undulating periodisation effectively functions to lessen the repeated bout effect, which states that the more the body is exposed to the same stimulus, the weaker the effect [9].

A number of individual studies suggest, compared with linear periodisation, there may be an advantage to applying daily undulating periodisation for strength development.  However, the available literature is far from definitive particularly among more athletic or highly trained populations.  General duration used in the available research is approximately 12-weeks, where longer term interventions would be required to assess the advantage of DUP over LP for strength improvement.  Fewer studies presently compare DUP with LP for muscle growth.  Only a few studies suggest that variable loading may prove more beneficial for muscle hypertrophy compared to constant loading.

For individuals beyond the beginner stages of resistance exercise, daily undulating periodisation is an excellent method for adding variety to one’s resistance training program to potentially increase strength and muscle growth.  Importantly, DUP and WUP models should be accepted as a template whereby an individual or personal trainer should still manipulate the design to fit their own or their clients training.

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References:

[1] Baker, D. et al. 1994. Periodisation: The Effect on Strength of Manipulating Volume and Intensity. Journal of Strength Conditioning Research. November. Vol 8, No. 4, pp. 235-242.

[2] Harries, S. K. 2015. Systematic Review and Meta-analysis of Linear and Undulating Periodized Resistance Training Programs on Muscular Strength. Journal of Strength and Conditioning Research. April. Vol. 29, No. 4, pp. 1113-1125.

[3] Kraemer, W. J. et al. 2003. Physiological Changes with Periodized Resistance Training in Women Tennis Players. Medicine and Science in Sports and Exercise. January. Vol. 35, No. 1, pp. 156-168.

[4] Miranda, F. et al. 2011. Effects of Linear vs. Daily Undulatory Periodised Resistance Training on Maximal and Submaximal Strength Gains. Journal of Strength Conditioning Research. July. Vol. 25, No. 7, pp.1824-1830.

[5] Poliquin, C. 1988. FOOTBALL: Five Steps to Increasing the Effectiveness of your Strength Training Program. National Strength & Conditioning Association Journal. June. Vol. 10, No. 3, pp.34 -39.

[6] Rhea, M. R. et al. A Comparison of Linear and Daily Undulating Periodised Programs with Equated Volume and Intensity for Strength. Journal of Strength and Conditioning Research. May. Vol 16, No. 2, pp. 250-255.

[7] Schoenfeld. B. J. 2016. Effects of Varied Versus Constant Loading Zones on Muscular Adaptations in Trained Men. International Journal of Sports Medicine. June. Vol. 37, No. 6, pp. 442-447.

[8] Schoenfeld, B. J. 2013. The M.A.X. Muscle Plan. Leeds: Human Kinetics.

[9] Zatsiorsky, V. M. & Kraemer, W. J. 2006. Science and Practice of Strength Training. Champaign, IL: Human Kinetics.

[10] Zourdos, M. C. et al. 2016. Modified Daily Undulating Periodisation Model Produces Greater Performance Than a Traditional Configuration in Powerlifters. Journal of Strength and Conditioning Research. March. Vol. 30, No. 3, pp. 784-791.

In resistance exercise, it is common to see wide variation in the way lifters squat.  Some lifters may squat more upright, while others may squat with outward turned feet, or with a wider stance.  Moreover, some lifters may be credited for squatting more vertically, while others criticised for using a more pronounced forward lean.  Difficulty with squatting is quickly criticised by suggesting poor technique or immobility in the hips, knees or ankles.  However, little, if any, consideration is given to anatomical variations in the hip or leg as influencers in squatting mechanics.

Basic Anatomy 

The upper limb describes the femur or thigh bone and the lower limb describes the tibia or shin bone [2].  The hip includes the pelvis and a socket on the pelvis known as the acetabulum [2].  The hip joint is where the head of the femur articulates with the acetabulum of the pelvis creating what is know as a ball-and-socket joint [2].

How Does Upper and Lower Limb Length Influence Squat Mechanics?

Squat mechanics can be greatly influenced by femoral (thigh bone) length [1, 3, 4].  Lifters with long femur lengths relative to shorter tibia (shin bone) lengths will naturally experience greater forward lean deeper into a squat compared to a lifter with proportional femur-to-tibia lengths [1, 3].  In these lifters, the hips require greater displacement (buttock pushed further backward) to allow for the weight and upper body to remain balanced over the centre of mass [3].  If this lifter were corrected to squat more upright, the lifter would simply fall backward [3].  Moreover, hip and knee flexion in this lifter can be completely normal, yet anatomical structure would prevent squatting with an upright posture [3].

Similarly, lifters with shorter or longer tibias relative to femur length will exhibit different squatting mechanics [1, 3, 4].  Shortened tiba length with long femur length would create greater hip displacement and cause forward lean deeper into the squat [1, 3]. Conversely, a lifter with longer tibia lengths relative to femur lengths would exhibit a more upright posture [3].  This lifter would feel more of quadriceps working during the squat, while a lifter with shorter tibias, relative to femur length, would feel greater effort in lower back musculature [3].

Restriction in the ankle joint, specifically in ankle dorsiflexion (bringing the foot upward) will further alter squat mechanics [1, 3].  Limited ankle dorsiflexion will prevent the knees from pushing forward during a squat and force the hips to displace backwards [3].  This would result in either an excessive forward lean, heels lifting off the ground, or simply reduced range of movement [3].

How Does Femoral Neck Angle Influence Squat Mechanics?

The femoral neck is the anatomical area between the head of the femur and shaft of the femur [2].  Femoral neck angle refers to the position at which the femoral neck inserts into the pelvis [2, 5].  There are three primary categories of femoral neck angle [2, 5]:

1. A femoral neck angle of 40-50 degrees
2. Coxa vara (more of a horizontal insertion into the pelvis)
3. Coxa valga (more of a vertical insertion into the pelvis)

Additionally, the femoral neck can be angled forward of the shaft of the femur in a position called anteversion [2, 5, 7].  Also, the femoral neck can be angled backward of the shaft of the femur in a position referred to as retroversion [2, 5, 7].  A study by Zalawadia and colleagues (2010) looked at 92 dry femur samples and found anteversion alignment differences of 20 degree or more between samples [7].

The implications of femoral neck angles in the squat relate to available range of movement.  For example, a lifter with 25 degrees of retroversion will experience early bone-on-bone contact in the squat as the femoral head comes into early contact with the acetabulum of pelvis [5].  In contrast, a lifter with 25 degrees of anteversion will be free of early bone contact and likely squat to a comparatively greater depth [5].

How Does Hip Socket Depth Influence Squat Mechanics?

In addition to variance in femoral neck angle and upper and lower limb sizes, people vary in the  depth of the hip socket (acetabulum of the pelvis) and thickness of femoral neck [5, 6].  The difference in hip socket depth and femoral neck thickness can further increase or decrease available range of movement when squatting [5, 6].  A lifter with shallow hip sockets and thin femoral necks will have greater available range of movement squatting compared to a lifter with deeper hip sockets and thicker femoral necks [5].

Furthermore, the angle at which the hip sockets are positioned will influence squat range of movement [5, 6].  In the photo below, the first pelvic sample shows outward facing hip sockets when compared to the second pelvic sample that exhibits more downward facing hip sockets [1, 5].  It is likely that a lifter with more outward facing hip sockets will benefit from a wider stance or a more externally rotated hip position for squatting, whereas a lifter with more downward facing hip sockets will benefit from a comparatively narrower stance [5].

Summary

When assessing squat mechanics, hip and upper and lower limb anatomy should absolutely be considered when understanding available range of movement.  Disproportional lengths between the femur, tibia and torso will result in altered mechanics that will likely prevent range of movement when squatting [1, 5].  Also, bone-on-bone contact in the hip joint will restrict range of movement and this contact will be genetically determined by the size, shape, position and alignment of a lifters hip joint [5].  In the occurrence of bone-on-bone contact during squatting, forcing more range will only result in trauma to the hip joint [5].  This is not to say that hip, knee and/or ankle mobility is not valuable, but to simply draw attention to the strong influence of anatomy on squat mechanics.

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References:

1. Bret Contreras., 2016. How Femur Length Affects Squat Mechanics [online]. [viewed 28 March 2017]. Available from: https://bretcontreras.com/how-femur-length-effects-squat-mechanics/.

2. Ellis, H. & Mahadevan, V., 2013. Clinical Anatomy. 13th Ed. Oxford: John Wiley & Sons Ltd.

3. Purvis, T., 2015 Squats Part 1: Fold-ability and Proportions [online]. [viewed 27 March 2017]. Available from: https://www.youtube.com/watch?v=Av3LO2GwpAk

4. Purvis, T., 2015 Squats Part 2: Fold-Ability and Proportions [online]. [viewed 27 March 2017]. Available from: https://www.youtube.com/watch?v=KGEKRjlZKf8

5. Somerset, D., 2015. No Two Hips Are The Same: How Anatomical Variance Can Affect Your Range Of Motion [online]. [viewed 29 March 2017]. Available from: https://bretcontreras.com/how-femur-length-effects-squat-mechanics/.

6. TMF., 2014. The Best Kept Secret: Why People HAVE to Squat Differently [online]. [ viewed 28 March 2017]. Available from: http://themovementfix.com/the-best-kept-secret-why-people-have-to-squat-differently/.

7. Zalawadia, A. et al. 2010. Study Of Femoral Neck Anteversion Of Adult Dry Femora In Gujarat Region. National Journal of Integrated Research in Medicine. Vol. 1, No. 3, pp. 7-11.

Exercise program design is considered both an art and a science.  The science is a critical part of the process, as prescription of any exercise variable requires an understanding of science-based principles [2]. In resistance training, these variables include: volume, intensity, tempo, rest intervals and frequency.  The successful achievement of a specific training outcome (i.e. hypertrophy, strength, power, muscular endurance) will be largely determined by proper manipulation of these training variables.  This article will provide a brief overview of each training variable and how such variables can be manipulated to achieve the desired training adaptation.

Exercise Program Design Variables

Volume

Volume in exercise program design describes the amount of exercise performed within a  specific time period [14].  For example, volume within a training session or over a weekly basis [12, 14]. Volume is defined as either [12, 14]:

(i) Total repetitions (sets x repetitions)
(ii) Volume load (sets x repetitions x resistance)

Repetitions

Training volume in exercise program design is prescribed according to the number of repetitions per set, number of sets per session, and the number of sessions per week [14].  Repetitions can be classified into three approximate ranges [12]:

1. Low (1 to 5)
2. Moderate (6 to 12)
3. High (15 or more)

Low repetitions are shown to be optimal for increasing muscle strength with minimal benefit to muscle hypertrophy [12].  Lifting at low repetition ranges allows for heavier weights to be used and for maximal muscular force and tension to be exerted [12].  Adaptions in muscular strength are associated with an improved response of the nervous system [12].  Motor units, which are individual neurons that innervate muscle fibers, become more synchronised and recruited in greater numbers under heavier loads [12]. Additionally, nerve impulses are stimulated at higher frequencies, all of which contribute to improved muscular strength [12].

Moderate repetitions (6 to 12) are optimal for muscle hypertrophy [2, 6].  This repetition range allows for increased tension to be exerted by the working muscles.  Also, at moderate repetitions, muscle tension is maintained long enough (time-under-tension) to enhance muscle damage and fatigue, both essential for muscle growth [12].

Using higher repetitions (15 or more) is better suited to achieving adaptations in muscular endurance (i.e. muscles ability to work sub maximally over a longer period) [12].  Working at higher repetition ranges requires less maximal force or muscle tension, however time-under-tension is enhanced from lifting over a longer duration [12].  The benefit of increased time-under-tension is an accumulation of metabolites in the blood (i.e. lactate, inorganic phosphate, hydrogen ions) that stimulate muscle protein synthesis and muscle growth [6].

Sets

A set in exercise program design is defined as a group of consecutive repetitions [8].  The literature shows that a single set performed to failure is enough to induce muscle hypertrophy and strength gains in both untrained and trained subjects [5].  However, a larger body of evidence supports the use of multiple sets over single sets for maximising muscle strength and growth.  A recent (2016) systematic review by Schoenfeld and colleagues showed a dose-response relationship whereby higher volumes (more sets per muscle per week) of resistance training resulted in greater hypertrophic gains compared to lower volumes [10].  As a general guideline for exercise program design, Schoenfeld recommends 2-4 sets per exercise, although this is more dependent on program design [12].  For time restricted training, lower volumes (<5 sets per muscle per week) is sufficient to gain muscle [13].  However, for those that can allocate more time to training, more sets (10+) per muscle per week, up to a certain limit, would lead to greater hypertrophy gains [10].

Intensity

Intensity, in the context of this article, is defined by load or the amount of weight lifted.  Among exercise variables, it is found to be the greatest driver of muscle hypertrophy and strength, even  more than volume [7, 12].  Intensity, in exercise program design, can be determined by repetition maximum (RM), defined by the maximum amount of weight lifted with correct technique for given number of repetitions [2].  For example, a 5RM is the maximum amount lifting with correct technique for five repetitions.

Training intensity, should be manipulated in exercise program design according to the desired goal and is generally determined by repetition range [2, 6].  For training goals related to increasing muscular strength, intensities of approximately 90 to 100 percent of 1RM is advocated [2, 12].  Heavier loads allow for maximal muscle force/tension to be generate, which is conducive to increasing muscular strength [12].  For example, someone with a 1RM squat of 50kg would use loads of 45kg to 50kg.  Training intensities for strength are generally applied within repetition ranges of 1 to 5 [12].

For training goals associated with muscle hypertrophy, moderate intensities of 65 to 85 percent 1RM are optimal for muscle development [12].  Moderate intensities allow for an ideal combination of sufficient muscle force/tension and time-under-tension that provide muscle fatigue and damage, both critical for muscle hypertrophy [12].  Repetition ranges of approximately 6 to 12 are associated with these intensities [2, 6, 12].

Lower intensities of approximately 60 percent or less are best suited to endurance related goals with less of an impact on hypertrophy or strength [12].  The build up of metabolites is advantageous for promoting muscle protein synthesis, however, muscle tension is considerably reduced compared with moderate or higher training intensities  [2, 6, 12].  Training intensities for endurance is typically applied to repetitions of 15 or more [12].

Tempo

Tempo or velocity in exercise program design refers to the speed at which repetitions are performed [6].

Tempo is divided into three different contractions [6]:

1. Eccentric (lowering)
2. Isometric (static)
3. Concentric (lifting)

This variable is expressed numerically in seconds and typically represented in four parts.  For example, a tempo of 2-1-0-1, would refer to a two second eccentric lowering, one second isometric hold in the bottom position, zero second concentric raise, and a one second isometric hold in the top position [8, 12].

For training adaptations related to improving strength, faster tempos (<1 second concentric, 1 second eccentric) have been found to be superior to slower tempos (1-2 seconds concentric, 1-2 seconds eccentric) [4,6].  Because force = mass x acceleration, intentionally slowing tempo would lead to reductions in force production as load would need to be lessened to compensate for a slower tempo [6].  Muscular force, particularly during the eccentric phase of a lift, is highly important for muscle hypertrophy, therefore using very slow tempos (i.e. 15 seconds per repetition) is counterproductive to muscle development [12].  Although, some research exists demonstrating that slower tempos can enhance protein synthesis (24-30 hours post workout), provided the lift is taken to failure [3].

As general guidelines for exercise program design, eccentric tempos of 2 to 3 seconds with an explosive concentric phase are beneficial for muscle growth [12].  However, the literature indicates wider ranges of tempos from 0.5 – 8.0 seconds per repetition can be applied for muscle hypertrophy [11].

Applying an isometric hold at either the bottom or top of a lift would increase time-under-tension, provided muscle tension is maintained, which may stimulate increased motor unit recruitment, muscle firing frequency, and force development [1].  Paused isometric holds at the bottom of a lift (i.e. squat or bench press) using high loads (>85 of 1RM) are commonly used to enhance strength gains.  As a general recommendation for exercise program design, maintaining constant tension at the bottom and top of a lift are suggested in contrast to applying longer isometric holds [12].

Rest Intervals

A rest interval in exercise program design is defined as the length of time between the end of one set to the start of another set or exercise [12].  Rest periods greatly influences the adaptive response to resistance training and its length is largely related to intensity (load) applied [6].  Rest intervals can be classified into three approximate ranges [12]:

1. Short – 30-60 seconds or less
2. Moderate – 1-2 minutes
3. Long – 3 minutes or more

Moderate rest intervals are beneficial for muscle hypertrophy and are found to be potent anabolic stimulators [6].  Hypertrophy training that uses moderate-to-heavy loads performed at moderate repetitions (6-12) rely primarily on energy provided by the adenosine triphosphate (ATP)- phosphocreatine (PCr) system and glycolysis [6].  These rest periods allow for metabolite accumulation in the blood (i.e. lactate), stimulation of anabolic hormones (i.e growth hormone, testosterone), and enhanced localised blood flow, all of which help to stimulate muscle growth [6].

Short rest intervals are best when training for muscular endurance [6, 12].  Endurance training that uses light loads performed at high repetitions (15 or more) primarily utilises aerobic metabolism for energy [6].  Training with short rest periods allows for enhanced metabolite accumulation, increased mitochondrial and capillary numbers and improved lactate buffering capacity [6, 12].

Although short and moderate rest intervals are beneficial for muscle endurance and hypertrophy, these rest periods have detrimental effects to strength and power [6].  Strength and power that uses heavy loads performed at low repetitions (1-6) rely on the ATP-PC energy system, which is best replenished with longer rest periods [6].  For strength, 2 minute rest intervals are advocated, while for power training, rest intervals of 4-8 minutes may be necessary to fully recuperate taxed energy systems [9].

Frequency

Training frequency in exercise program design refers to the number of training sessions completed within a specified period (i.e. one week) [2].  The duration between gym sessions is critical for ensuring sufficient muscular and neurological recovery [2].  Another aspect of great importance is selecting training frequencies to maximise protein synthesis [12].  Returning to the gym before the body has recuperated can severely impair protein synthesis as muscle damage persists [12].  Moreover, impairing the body’s recovery will negatively impact force production and the amount of weight that can be lifted in subsequent
training sessions [12].

Amongst the untrained, a training frequency of 1-3 days per week is found to promote muscular adaptations [2].  As training experience increases, research shows that frequencies of 3-4 days per week may be required to elicit further training adaptations [2].  Among advanced weightlifters and bodybuilders, frequencies of 4-6 days or more per week are found to enhance strength and metabolic adaptions [6].  However, the organisation of workouts at higher-frequencies of training become increasingly important to avoid overtraining [2, 6].

Weekly training frequency directly impacts total training volume [12].  For example, if within-session training volume remains constant and the number of training sessions are increased, total training volume will increase.  The danger with increasing frequency under these circumstances is an increased risk of overtraining [12].  Given this, exercise program design, using either split routine or total-body training, should be structured to ensure adequate recovery.

As a general recommendation for exercise program design, Schoenfeld recommends at least 3 training sessions per week to maximise muscle hypertrophy and a minimum of 48 hours between sessions that train the same muscle group [12].

Summary

Exercise program design is a complex process that involves manipulation of multiple variables.  Some of these variables include volume, intensity, tempo, rest intervals, and frequency.  The scientific literature provides highly valuable information as to how these variables should be manipulated to accelerate and maximise the desired training adaptation.  Prior to engaging in resistance training, an individual or personal trainer should consider the desired objective then apply evidence-based guidelines to justify exercise prescription.

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References:

[1] Behm, D. and Sale, D.G. 1993. Intended rather than actual movement velocity determines velocity-specific training response. Journal of Applied Physiology. January. Vol. 74, No.1, pp. 359-368.

[2] Bird, S. P. 2005. Designing Resistance Training Programmes to Enhance Muscular Fitness. Sports Medicine. Vol. 35, No. 10, pp. 841-851.

[3] Burd, N. A. 2012. Muscle time under tension during resistance exercise stimulates differential muscle protein sub-fractional synthetic responses in men. The Journal of Physiology. January. Vol. 590 (Part 2), pp. 351-362.

[4] Hay, J. G. 1983. Effects of lifting rate on elbow torques exerted during arm curl exercises. Medicine and Science in Sports and Exercise. Vol. 15, No. 1, pp. 63-71.

[5] Kladir, Z. A. 2014. Single- Versus Three-Set Resistance Training on Strength and Power Among Untrained Men. Proceedings of the International Colloquium on Sports Science, Exercise, Engineering and Technology. pp. 177-187.

[6] Kraemer, W. J. 2004. Fundamentals of resistance training: progression and exercise prescription. Medicine and Science in Sports and Exercise. April. Vol. 36, No. 4, pp. 674-688.

[7] McDonagh, M. J. 1984. Adaptive response of mammalian skeletal muscle to exercise with high loads. European Journal of Applied Physiology and Occupational Physiology. Vol. 52, No. 2, pp. 139-155.

[8] Poliquin, C. 1997. The Poliquin Principles. Napa: Daton Writers Group.

[9] Raastad, T. et al. 2000. Hormonal responses to high- and moderate-intensity strength exercise. European Journal of Applied Physiology. May. Vol. 82, No. 1-2, pp. 121-128.

[10] Schenfeld, B. J. 2016. Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis. Journal of Sports Sciences. July. Vol. 19, pp. 1-10.

[11] Schoenfeld, B. J. 2015. Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis. Sports Medicine. April. Vol. 45, No. 4, pp. 577-585.

[12] Schoenfeld, B. J. 2013. The M.A.X. Muscle Plan. Leeds: Human Kinetics.

[13] Schoenfeld, B. J. 2013. How Many Sets Do You Need to Perform to Maximize Muscle Gains? [Online]. [viewed on February 20, 2017]. Available from: http://www.lookgreatnaked.com/blog/how-many-sets-do-you-need-to-perform-to-maximize-muscle-gains/.

[14] Tan, B. 1999. Manipulating Resistance Training Variables to Optimise Maximum Strength in Men: A Review. Journal of Strength and Conditioning Research. Vol. 13, No. 3, pp. 289-304.

Introduction

Muscle building is an objective shared by both male and females that engage in resistance exercise (i.e. free weights, cable pulleys, resistance machines).  It is well accepted that the process of muscle growth involves the signalling of anabolic pathways that promote protein synthesis (building of new muscle protein) and prevent muscle breakdown [5].

Current research indicates that three primary mechanisms are involved in the muscle building process [5, 7].  These mechanisms include mechanical tension, metabolic stress and muscle damage [7].  A basic understanding of these mechanisms can help to inform exercise programme design to maximise muscle growth.

Mechanisms of Muscle Building

Mechanical Tension

Prevailing research indicates that mechanical tension is the primary driver of muscle hypertrophy [7].  Mechanical tension relates to the force and stretch generated by muscles during resistance exercise [7, 8].  During weight lifting, muscle tension develops when the weights are lowered (eccentrically), which in turn increases the tension on the contractile components of muscle (actin and myosin), resulting in a hypertrophic response [7].

Also, muscle tension during resistance exercise has been shown to interrupt the integrity of the working muscles [5].  This interruption brings about mechanical and chemical signals in the muscle that activate anabolic pathways and promote muscle growth [7].  Greater muscle tension achieved by increasing the load lifted can elicit a stronger anabolic stimulus [7].  However, an upper threshold exists whereby continually increasing tension will have diminishing returns (i.e. overtraining) [5].

From a practical application standpoint, utilising a repetition range of 1 to 5 repetitions and loads of 90 to 100 percent of 1-repetition maximum (1RM) would be appropriate to enhance mechanical tension [5].  Training in this lower rep range and with heavier weights will generate improvements in strength as the nervous system becomes better coordinated and synchronised [5].

Metabolic Stress

Metabolic stress manifests as a results of metabolites that build up in the bloodstream from resistance training [5].  These metabolites include lactate, hydrogen ion, inorganic phosphate, creatine, and others.  The specific mechanisms why metabolic stress increases muscle hypertrophy is completely understood.  However, there are several suggested theories:

Type I and II Fiber Type Stimulation

1. All muscles are made up of muscle fibers that contract when stimulated.  The two basic fiber types being fast-twitch (type II) and slow-twitch (type  I) [3, 5].  Fast-twitch fibers show a greater potential for growth compared to slow-twitch fibers (about 50% more), yet increased activation of both types will maximise muscle hypertrophy [3].  Research shows that metabolic stress enhances muscle hypertrophy by activating and fatiguing slow-twitch muscle fibers then forcing activation of fast-twitch fibers [6].

Cell Swelling

2. The feeling of muscles being “pumped” during resistance exercise is a phenomenon known as cell swelling [5].  Research shows that cell swelling promotes muscle growth by stimulating protein synthesis and decreasing protein breakdown [6, 7].  Cell swelling occurs because of metabolic stress and primarily because of the lactate build-up in the blood [4, 6].  Lactate encourages water to be drawn into the muscle cell, which in turn places pressure on the cell wall [6, 7].  The muscle cell perceives this pressure as a threat to its structure and in response, sends anabolic signals that strengthens the cell [6, 7].

Growth Factors

3. Muscle tissue produces a number of growth enhancing substances [4].  Metabolic stress training is shown to increase a specific growth factor called mechano-growth factor (MGF), which is found to be important in muscle hypertrophy [5].  Other growth factors including interleukin and fibrobrast growth factors have been found to activate from metabolic stress, which can further contribute to muscle building [4].

From a practical application standpoint, metabolic stress is achieved by using higher repetitions (15-20 reps) range and loads of 60 percent or less of 1RM [5].  Training in this higher repetition range will target more muscular endurance with little effect on muscle building because of the minimal activation of fast-twitch muscle fibers [5].

Muscle Damage

The familiar muscles soreness felt approximately 24 hours to 2-3 days following resistance training is known as delayed onset muscle soreness (DOMS) [1].  DOMS is caused by small tears in the working muscle at a micro level [1, 2].  In response to damaged muscle tissue, immune cells (i.e. macrophages) migrate to the area to remove debris and repair the cell structure [1, 7].  When this occurs, macrophages produce signalling molecules called cytokines [1, 2, 7].  These cytokines release certain growth factors that promote muscle building [5, 7].  The end results is a stronger cell structure that can better withstand future muscle damage [5, 7].

Muscle soreness is not required for muscle building [5].  The more an individual trains at higher intensities, the better the tolerance to muscle soreness [5].  However, even in the absence of muscle soreness, damage to the fibers still occurs [5].  A point exists where too much muscle damage can be detrimental to muscle building.  If muscle soreness is too great, this can delay the recovery of working muscle, which is essential for muscle building [5].

From a practical application standpoint, a moderate repetition range between 8 to 12 repetitions and loads of between 65 to 85 percent of 1RM is optimal to create muscle damage [5].  This repetition range allows for greater muscle tension to be sustained long enough to enhance muscle damage and fatigue [5].  This moderate repetition range can also generate accumulation of metabolite, which can further contribute to enhanced muscle building [5].

Summary

A common goal in exercise is the development of lean muscle.  The great majority with this objective use moderate ranges (8-12 repetitions) with resistance training.  However, research shows that certain gym programmes will encourage muscle building more than others.  An examination of the research reveals three primary mechanisms that maximise muscle building.  These mechanisms include mechanical tension, metabolic stress and muscle damage.  Activation of each mechanism is best achieved by varying repetition range and load.  Given this, individuals that want to maximise muscle building should try to vary their resistance training programmes to integrate low repetition (1 to 5) with heavy loads (90% to 100% of 1RM), moderate repetitions (8 to 12) with moderate loads (65% to 85% of 1RM), and finally high repetitions (15 to 20) with light loads (<60% of 1RM).

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References:

[1] MacIntyre, D. L. et al. 1995. Delayed muscle soreness. The inflammatory response to muscle injury and its clinical implications. Sports Medicine. July. Vol. 20, No. 1, pp. 24-40.

[2] Mizumura, K. & Taguchi, T. 2016. Delayed onset muscle soreness: Involvement of neurotrophic factors. The Journal of Physiological Sciences. January. Vol. 66, No. 1, pp. 43-52.

[3] Schoenfeld, B. J. 2016. Science and Development of Muscle Hypertrophy.  Australia: Human Kinetics.

[4] Schoenfeld, B. J. 2013. Potential Mechanisms of a Role of Metabolic Stress in Hypertrophic Adaptations to Resistance Training. Sports Medicine. March, Vol. 43, No. 3, pp. 179-194.

[5] Schoenfeld, B. J. 2013. The M.A.X. Muscle Plan. Leeds: Human Kinetics.

[6] Schoenfeld, B. J. 2013. The Role of Metabolic Stress in Muscle Growth [Online]. [Viewed 25 December 2016]. Available from: http://www.lookgreatnaked.com/blog/the-role-of-metabolic-stress-in-muscle-growth/

[7] Schoenfeld, B. J. 2010. The Mechanisms of Muscle Hypertrophy and their Application to Resistance Training. Journal of Strength and Conditioning Research. October, Vol. 24, No. 10, pp. 2857-2872.

[8] Toigo, M and Boutellier, U. 2006. New fundamental resistance exercise determinants of molecular and cellular muscle adaptations. European Journal of Applied Physiology. August, Vol. 97, No. 6, pp. 643–663.