The effect of trunk and shank position on the hip-to-knee moment ratio in a bilateral squat.

Objectives: The effect of knee position on joint moments during squats has been studied; however, the effect of trunk angle has been less well investigated. This study evaluated the effect of both trunk and knee sagittal plane position on the distribution of moments between the hip and knee extensors during the bilateral squat.

Design: Observational study.

Setting: Biomechanics laboratory.

Participants: One hundred individuals performed bilateral squats.

Main Outcome Measures: Motion and force data were collected using motion capture and force plates. Trunk and shank angles and hip and knee moments were calculated. A linear regression was used to associate the ratio between the hip and knee moments (hip-to-knee moment ratio) with the sagittal plane trunk and shank angles, while accounting for six squat depths (between 60° and 110° of knee flexion) and side.

Results: Trunk angle and shank angle each contributed to the hip-to-knee moment ratio (P < .001) with trunk accounting for a higher proportion of variance than the other variables. The hip-to-knee moment ratio increased with increasing trunk angle and with decreasing shank angle.

Conclusions: This large cohort study supports the use of trunk position to instruct squat technique with the goal of modifying hip and knee moments.