Influence of Relative Hip and Knee Extensor Muscle Strength on Landing Biomechanics

STEARNS, K. M., R. G. KEIM, and C. M. POWERS. Influence of Relative Hip and Knee Extensor Muscle Strength on Landing Biomechanics. Med. Sci. Sports Exerc., Vol. 45, No. 5, pp. 935-941, 2013. Purpose: This study aimed to determine whether the tendency of women to exhibit higher knee extensor moments relative to hip extensor moments during the deceleration phase of landing can be explained by the relative strength of the knee and hip extensors. Methods: Forty recreationally active individuals participated in this study (20 men and 20 women). The maximum isometric strength of the knee extensors and hip extensors was assessed using a load cell and custom testing setup. Lower extremity kinematics and kinetics were collected during a double-leg drop-jump task. Results: When compared with men, women demonstrated a significantly higher knee-hip extensor moment ratio during the deceleration phase of landing (1.42 +/- 0.6 vs 1.12 +/- 0.3, P < 0.001). In addition, the knee-hip extensor isometric strength ratio was significantly higher in women compared with men (1.01 +/- 0.2 vs 0.89 +/- 0.2, P < 0.001). The Pearson partial correlation (controlling for sex) revealed a significant positive association between the knee-hip extensor isometric strength ratio and the knee-hip extensor moment ratio (r = 0.41, P = 0.005). Conclusion: The tendency of women to exhibit higher knee extensor moments relative to hip extensor moments may be explained, in part, by the relative strength of the hip and knee extensors.