Joint Laxity Is Related to Lower Extremity Energetics during a Drop Jump Landing

SHULTZ, S. J., R. J. SCHMITZ, A. NGUYEN, and B. J. LEVINE. Joint Laxity Is Related to Lower Extremity Energetics during a Drop Jump Landing. Med. Sci. Sports Exerc., Vol. 42, No. 4, pp. 771-780, 2010. Purpose: To examine the relationships between anterior knee laxity (AKL), genu recurvatum (GR), and general joint laxity (GJL) with sagittal plane energetics in males and females during a drop jump task. Methods: A total of 68 females and 50 males were measured for AKL, GR, and GJL and were instrumented to obtain neuromuscular and biomechanical data on their dominant limb during the initial landing phase of a 45-cm drop jump. Multiple linear regressions determined the extent to which the three joint laxity variables combined to predict hip, knee, and ankle work absorption and stiffness. Associations between joint laxity and joint kinematics, joint kinetics, and muscle activation amplitudes were also investigated to further interpret significant relationships. Results: Higher AKL and GJL and lower GR combined to predict greater knee work absorption (R-2 = 0.210, P = 0.002) and stiffness (R-2 = 0.127, P = 0.033) and lower ankle stiffness (R-2 = 0.115, P = 0.048) in females. These associations were modulated through greater peak knee extensor moments and flexion angles, lower hamstring activation, and lower ankle extensor moments. In males, joint laxity had little impact on knee energetics, but a significant association was observed between greater GJL and decreased ankle stiffness (R-2 = 0.209, P = 0.012), a product of both greater peak ankle flexion and decreased ankle extensor moment. Conclusions: Females with greater AKL and GJL and lower GR demonstrated a landing strategy that increased work absorption and stiffness about the knee, whereas females with greater GR demonstrated a landing style that reduced knee work absorption and stiffness. The findings suggest that AKL, GR, and GJL may represent distinct risk factors and support the need to consider more comprehensive laxity profiles as they relate to knee joint function and anterior cruciate ligament injury risk.