Optimizing Clinical Assessment of Knee Function: Biomechanical Adaptations Across Repeated Single-Leg Hop Trials

Single-leg hop performance is widely used in clinics to assess knee function following anterior cruciate ligament injury. However, performance provides limited insight into joint-specific kinetic contributions, and the influence of repeated trials remains unclear. This study quantified the effects of hop directions (forward/vertical/backward) and repeated practice trials on performance and lower-limb joint kinetics. Forty-five injury-free participants performed 10 trials per task. Hop performance and peak moment/power/work at the hip/knee/ankle were calculated. Trials were grouped as one practice attempt and 3 blocks: I (trials 2-4), II (trials 5-7), and III (trials 8-10). Three-by-three repeated-measures analyses of variance were conducted to quantify the effects of task and practice. Backward hop demonstrated the greatest knee moment/work/power and contribution across blocks. Performance increased across blocks in forward and backward hops while remaining consistent in the vertical hop. Knee work was smaller in block I across tasks, whereas backward hop demonstrated greater knee work contribution in block II than in block I. The backward hop places greater knee emphasis, supporting its use as a knee-specific assessment. Minimal practice trials are necessary when using forward/vertical/backward hop performance to assess knee power, whereas at least 4 trials may be required for forward and vertical hops when evaluating knee work.