BACKGROUND: Literature shows that landing with great impact forces may be a risk factor for knee injuries. The purpose of this study was to examine the relationships among selected lower extremity kinematics and kinetics during the landing of a stop-jump task. METHODS: Landmark coordinates and ground reaction forces during a stop-jump task were collected. Lower extremity joint angles and resultants were reduced. Pearson correlation coefficients among selected lower extremity kinematics and kinetics were determined. FINDINGS: The hip flexion angular velocity at the initial foot contact had significant correlation with peak posterior and vertical ground reaction forces (r = -0.63, P < 0.001, r = -0.48, P < 0.001) during the landing of the stop-jump task. The knee flexion angular velocity at the initial foot contact also had significant correlation with peak posterior and vertical ground reaction force (r = -0.49, P < 0.001, r = -0.06, P < 0.001) during the landing of the stop-jump task. Peak proximal tibia anterior shear force and peak knee extension moment during landing of the stop-jump task had significantly correlation with the corresponding posterior and vertical ground reaction forces (r > 0.51, P < 0.001). INTERPRETATION: A large hip and knee flexion angles at the initial foot contact with the ground do not necessarily reduce the impact forces during the landing of the stop-jump task, but active hip and knee flexion motions do. Hip joint motion at the initial foot contact with the ground appears to be an important technical factor that affects anterior cruciate ligament loading during the landing of the stop-jump task.
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