The Effect of Fatigue, Velocity and Interaction of Them on the Inter-Muscular Coordination of Hamstring and Quadriceps Muscle

Due to aspect of biomechanical and neuromuscular, intermuscular coordination have a major role in function of knee joint and prevention of knee joint injuries. The purpose of this study was to characterize the effect of velocity and fatigue on the intermuscular coordination of hamstrings and quadriceps muscles. This study is quasi-experimental that was done on 31 healthy and non-athletic subjects (24 women, 7 men) aged between 20-30 years. They were selected by convenience non-probable sampling method. Subjects performed sixty knee flexion and extension with maximum voluntary effort at the velocity of 45°/s. Surface EMG of quadriceps and hamstring muscles was recorded for the study of EMG onset time during extension of the knee joint in the velocities 45°/s, 150°/s and 300°/s by isokinetic dynamometer before and after fatigue. Then data were compared. The findings showed in various velocities of fatigue and non fatigue conditions, EMG onset of hamstring muscles related to quadriceps muscles are delayed. The average of these delayed time decreased with increasing velocity in non-fatigue condition: 45°/s=74.3±13.2 ms, 150°/s=50±7.5 ms, 300°/s=53.8±7.2 ms (p<0.05) and in fatigue condition: 45°/s=68±8.8 ms, 150°/s=50.8±11.6 ms, 300°/s=48.3±4.4 ms) did not change with increasing velocity. The results of this research showed that higher velocity have more effect on delay onset time of hamstrings and quadriceps muscles activations. In fact, we can say that significant changes are related to effect of velocity not fatigue.