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.