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.