ABSTRACT
BACKGROUND: Eccentric quadriceps contraction during landing and the resulting anterior tibial shear force are anterior cruciate ligament injury risk factors, while hamstring contraction limits anterior cruciate ligament loading. Anterior tibial shear force is derived from quadriceps and hamstring co-contraction, and a greater quadriceps/hamstring strength ratio has been associated with heightened lower extremity injury risk. The purpose of this investigation was to evaluate relationships between anterior tibial shear force during landing and quadriceps and hamstring strength. METHODS: Anterior tibial shear force was calculated during a jump landing task in 26 healthy females. Isokinetic eccentric quadriceps strength and concentric hamstrings strength were assessed at 60 degrees /s, 180 degrees /s, and 300 degrees /s. Correlational analyses were conducted to evaluate relationships between lower extremity strength and anterior tibial shear force. FINDINGS: Quadriceps (r=0.126 to 0.302, P>0.05) and hamstrings strength (r=-0.019 to 0.058, P>0.05) and the quadriceps/hamstring ratio (r=0.036 to 0.127, P>0.05) were not significant predictors of anterior tibial shear force. INTERPRETATION: Quadriceps and hamstring strength are not indicative of sagittal-plane knee loading during landing. Contractile force resulting from maximal strength testing may not represent that produced during landing, as it is unlikely that landing requires maximal effort. Additionally, peak anterior tibial shear force, quadriceps torque, and hamstrings torque are generated at different points in the knee flexion/extension range of motion. Therefore, peak anterior tibial shear force is a function of the available strength at a given point in the range of motion rather than of peak strength. These findings illustrate the limitations of peak strength values in predicting dynamic loading during landing.
