The aim of this study was to determine the relative muscular effort (RME) during the barbell back squat exercise. The authors wanted to understand the effects of barbell load and squat depth on hip extensor, knee extensor, and ankle plantar flexion RME. Due to the challenge of directly measuring muscle force, motion analysis techniques were used in combination with equations of motion to solve for the net joint moment (NJM). The net joint moment helps "provide an estimate of the minimum muscular torque required at a joint."
Previous studies have found that hip extensor NJM was increased with barbell load increased relative to knee extensor NJM. In addition, other studies have found that knee extensor NJM increased with increased squat depth relative to hip extensor NJM. What these previous studies have shown is that squat depth and barbell load require different muscular efforts of different muscle groups.
Ten college aged women with a minimum 1 year high-bar barbell squat experience and ability to perform a deep squat with greater than or equal to 1x their body weight participated in this study. Three sessions were performed: 1. Back squat 1RM test, 2. Motion analysis of back squat, 3. Maximum isometric strength test.
What was found is that barbell load does not affect knee extensor RME whereas squat depth significantly increased knee extensor RME, particularly between 105-119 degrees. Hip extensor RME was found to be greatest when both squat depth and barbell load were greatest.
What we can take away from this study is the importance of squat depth. Too often we see athletes perform only the top 1/4-1/2 of a barbell squat and load up the weight. Teaching the basics of proper squat depth and ensuring that athletes have that range of motion in the hips, knees, and ankles to perform a correct squat depth is very functional. Consider the results of this study when creating resistance programs for athletes and proper use of the squat depth & barbell load variables when determining the needs analysis of the athletes.