BACKGROUND: For reducing the high prevalence of anterior cruciate ligament (ACL) injuries, the sports instruction by changing biomechanical indices may be effectively. This study aimed to investigate the effect of knee middle position instruction (KMPI) on knee biomechanics during a landing task. Action guidance can prevent ACL injury by changing the biomechanical index of knee joint METHODS: Seventeen female collegiate volleyball athletes were recruited to the study. Kinematic, kinetic, and electromyography data were collected during single leg landing and compared before and after KMPI. The associations among the alteration in knee angle, knee torque, and muscle activity during the preactivity and postcontact phases were statistically analyzed. RESULTS: After KMPI, the participants had: 1) a reduced knee abduction angle at initial ground contact time (mean =-1.2°, P<0.05); 2) decreased maximum knee abduction torque (mean =0.1 Nm/kg/m, P<0.05); and 3) an increased maximum knee flexion angle (mean =5.4°, P<0.05). After KMPI, quadriceps preactivity alteration and hamstrings activity alteration were correlated with knee extension torque alteration (r=0.72, P<0.01 and r=-0.50, P<0.05, respectively). CONCLUSIONS: KMPI was designed to correct the knee alignment during the single leg landing, which may decrease the ACL injury risk.
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