C-18 Free Communication/Slide - Sport Biomechanics 1: MAY 29, 2008 8:00 AM - 10:00 AM ROOM: 122
Neuromuscular fatigue has been demonstrated to produce abnormal landing strategies, which may increase non-contact anterior cruciate ligament (ACL) injury risk. However, the precise impact of simultaneous quadriceps and hamstring (QH) muscle fatigue, whose synergistic actions are central to safe landing, is unclear. Elucidating the impact of QH fatigue on lower limb landing mechanics may aid in formulating more effective prevention regimens that can combat the deleterious impact of fatigue.
PURPOSE: To examine the effects of QH fatigue on lower extremity mechanics during single-leg forward hopping.
METHODS: Twenty-five healthy male (n=13; height 1.8±0.1m; mass 76±8.9kg) and female (n=12; height 1.7±0.1m; mass 58.3±7.7kg) volunteers performed three single-leg forward hops onto a force platform before and after substantial QH fatigue. Fatigue was induced through sets of alternating QH concentric contractions on an isokinetic dynamometer until subjects performed the first five repetitions of a given set below 50% of their QH peak torque. Three dimensional hip and knee kinematics and kinetics were quantified for pre- and post-fatigue landing trials, from which mean subject based measures were determined at initial contact (IC) and peak vertical ground reaction force (vGRF). Repeated measures mixed models ANOVAs were used to test for the main effect of fatigue.
RESULTS: Fatigue produced significant increases in IC hip internal rotation (pre-fatigue 0.28±7.42°, post-fatigue 3.5±7°, P=0.02), knee flexion (pre-fatigue 13.38±5.36°, post-fatigue 7.42±6.31°, P=0.001) and external rotation (ER) angles (prefatigue 0.29±2.89°, post-fatigue -2.38±5.56°, negative indicating ER, P=0.04). Fatigue-induced changes in knee flexion (pre-fatigue 25.4±8.76°, post-fatigue 19.14±8.82°, P=0.002) and ER (pre-fatigue 0.27±3.37°, post-fatigue -2.34±5.62°, P=0.02) angles were also evident at peak vGRF. Smaller peak vGRF external knee flexion (pre-fatigue 0.8±0.63 Nm, post-fatigue 0.29±0.38 Nm, P=0.002) and ER (pre-fatigue 0.14±0.12 Nm, post-fatigue 0.07±0.11 Nm, P=0.04) moments existed post-fatigue.
CONCLUSION: Isolated QH fatigue results in altered hip and knee neuromechanics that may increase ACL injury risk, suggesting that fatigue-resistance training within prevention programs may be warranted.