The center of pressure position in combination with ankle dorsiflexion and trunk flexion is useful in predicting the contribution of the knee extensor moment during double-leg squatting

BACKGROUND: Squatting exercises are commonly used in rehabilitation for knee joint disorders; in these exercises, control of knee extensor moment is important to enhance training effects and to avoid adverse effects. Ankle dorsiflexion and trunk flexion are widely used to reduce knee extensor moments during squatting, but the increased load on the low back is a concern. The purpose of this study was to determine whether the anterior–posterior (AP) center-of-pressure (COP) position and the AP-COP position in combination with ankle dorsiflexion and trunk flexion angles can predict the contribution of the knee extensor moment during double-leg squatting. METHODS: Twenty-eight healthy individuals (14 female and 14 male participants, age 22.8 ± 1.3 years) performed three sets of five consecutive double-leg squats. Kinematics and kinetics were analyzed using a three-dimensional motion analysis system with force plates. Univariate and multivariate regression analyses were performed to predict the contribution of the knee extensor moment (% total support moment) from AP-COP position, ankle dorsiflexion, and trunk flexion. RESULTS: The AP-COP position was a significant predictor of the knee extensor moment contribution (R(2) = 0.168, P = 0.030). Multivariate analysis showed that the ankle dorsiflexion angle (ΔR(2) = 0.561, β = 0.842) and AP-COP position (ΔR(2) = 0.296, β = − 0.499) predicted the knee extensor moment contribution (model R(2) = 0.857, P < 0.001). Additionally, the combination of trunk flexion (ΔR(2) = 0.429, β = − 0.613) and AP-COP position (ΔR(2) = 0.109, β = − 0.332) predicted the knee extensor moment contribution (model R(2) = 0.538, P < 0.001). The limb symmetry index of the knee extensor moment was significantly associated with that of the AP-COP position (R(2) = 0.493, P < 0.001) but not with that of the ankle dorsiflexion angle (P = 0.057). CONCLUSIONS: The AP-COP position can predict the contribution of the knee extensor moment and improve the prediction when combined with ankle dorsiflexion and trunk flexion. The present findings suggest that intervention focusing on the AP-COP position in combination with ankle dorsiflexion or trunk flexion would be useful to coordinate the contribution of the knee extensor moment during double-leg squatting.