Review: Lower Extremity Strength and the Range of Motion in Relation to Squat Depth
Squats are a relatively common exercise, often used to increase lower body strength (Kim, et al, 2015). When used in weightlifting and powerlifting, high flexion angles are required in the hips, knees, and ankles, which may increase musculoskeletal stress or knee injury (Kim, et al, 2015). Mediolateral rotation of the hip, knee alignment inside or outside of the hip during the squat can also increase the compressive and shear forces occurring at the ankle, knee, and hip (Kim, et al, 2015).
Decreased hip and ankle musculature strength have been reported to reduce stability of the lower extremity, which can in turn result in faulty alignment of the lower extremities (adduction and rotation of the hip, knee valgus) (Kim, et al, 2015). Activation of the tibialis anterior muscle is needed to initiate the squat, and the rectus femoris serves as both a hip flexor and a stabilizer of the hip and knee (Kim, et al, 2015).
Because squatting involves multiple joints, performance of the squat requires both strength and mobility of the hip, knee, and ankle (Kim, et al, 2015). Previous studies have shown deficits in dorsiflexion led to decreased peak knee flexion and increased knee valgus, while lifters with medial knee displacement during a squat exhibit tight and weak ankle musculature (Kim, et al, 2015).
One hundred and one participants were assessed by the same examiner. Both passive and active range of motion were measured at the hip, knee, and ankle with a universal goniometer. The examiner measured hip flexion, hip internal and external rotation, ankle dorsiflexion (while the knee was both flexed and extended). Strength of the hip flexors and dorsiflexors were measured with a hand-held dynamometer. Additionally, participants performed a bodyweight squat to their maximum depth (with heels flat on the floor) with their hands behind their heads, and this position was photographed.
In males, hip flexion, internal rotation, and ankle dorsiflexion in both knee positions were negatively correlated with squat depth. In females, Dorsiflexion in both knee positions was negatively correlated with squat depth, but dorsiflexor strength was positively correlated with squat depth. For males, ankle dorsiflexion with a flexed knee and hip flexion ROM were predictor variables for squat depth. For females, ankle dorsiflexion with an extended knee and dorsiflexor strength were predictor variables for squat depth.