Tibiofemoral joint kinetics during squatting with increasing external load.

CONTEXT There is limited information about the effects of increasing load while squatting. OBJECTIVE To quantify tibiofemoral joint kinetics during squatting with variable loads. SETTING Research laboratory. PARTICIPANTS 20 male students. INTERVENTION Tibiofemoral joint kinetics and electromyographic (EMG) activity of four involved muscles were determined by recording the half squat with variable external loads. MAIN OUTCOME MEASURES Tibiofemoral joint force and external moment components and EMG activity of four involved muscles. RESULTS Throughout the exercise, a posterior direction for the antero-posterior shear force and a net extension for the external moment were observed. They increased with knee flexion reaching peak force of 29% of the subject body weight (BW) and moment of 88Nm (without external load). All force and moment components and muscle activities increased as the external load increased. CONCLUSION These findings suggest that half squat may be safe to use for quadriceps strengthening with very low potential loading on the anterior cruciate ligament (ACL). Our data can help clinicians choose the appropriate external load.