Abstract / Summary
The quadriceps and hamstring muscles play a central role in absorbing impact forces and maintaining dynamic knee stability during landing tasks. Together, these muscle groups also strongly influence knee joint kinematics and kinetics. This study aimed to compare the effects of induced fatigue of the quadriceps and hamstring muscles on the kinematics and kinetics of the knee joint during a single-leg landing in a forward-drop jump task. Of the 108 athletes (aged 20–25 years) randomized to either the quadriceps or hamstring fatigue group, 93 completed the study and were analyzed. The peak knee flexion angle, vertical ground reaction force (vGRF), anterior tibial shear force, and knee flexion-extension and abduction-adduction moments were measured before and after inducing fatigue in the quadriceps or hamstrings during a forward-drop jump with a single-leg landing. Hamstring fatigue significantly reduced the peak knee flexion angle ( p < 0.001) compared with quadriceps fatigue. Also, hamstring fatigue significantly increased the vGRF and anterior tibial shear force ( p < 0.001) more than quadriceps fatigue. The peak flexion moment demonstrated a significant Group × Time interaction ( p = 0.022), decreasing significantly following hamstring fatigue ( p < 0.001). Conversely, the peak extension moment showed a significant Group × Time interaction ( p < 0.001), decreasing significantly following quadriceps fatigue ( p < 0.001). The knee abduction and adduction moments were significantly affected ( p < 0.001) by quadriceps fatigue more than by hamstring fatigue. Hamstring fatigue was associated with greater changes in knee flexion angle, vertical ground reaction force, anterior tibial shear force, and peak flexion moment, whereas quadriceps fatigue induced more disturbances in knee abduction and adduction moments. These findings highlight distinct, muscle-specific changes in surrogate biomechanical measures that reflect different mechanical pathways associated with ACL loading. The trial was registered on 5/5/2023, Iranian Registry of Clinical Trial, Identifier: (IRCT20230329057784N1).