The effect of fatigue and velocity on the relative timing of hamstring activation in relation to quadriceps

Inter-muscular coordination has an important role in proper function and prevention of injuries in the knee joint. The purpose of this study was to characterize the effect of velocity and fatigue on the relative activation onset of hamstring to quadriceps muscles during knee extension. Thirty one healthy and non-athletic volunteers (24 women, 7 men) were recruited for the study. The onset time of vastus medialis, vastus lateralis, rectus femoris, medial and lateral hamstring were measured during maximum voluntary extension of the knee joint at velocities of 45° /s, 150° /s & 300° /s before and after fatigue and the mean delay onset of all pairs of H-Q were measured. A two-way repeated measures ANOVA test was used to compare across the mean delayed onset of hamstring related to quadriceps muscles at various velocities. Hamstring muscle showed a delayed activation related to quadriceps and increasing the velocity of shortening has a prominent effect on the inter-muscular coordination with early activation of hamstring related to quadriceps muscles (F = 6.7, p < 0.002 for Biceps-rectus femoris, F = 6.31, p < 0.003 for semitendinosus-rectus femoris, F = 6.26, p < 0.003 for biceps-vastus lateralis, F = 5.98, p < 0.004 for semitendinosus-vastus lateralis, F = 3.19, p < 0.04 for biceps-vastus medialis and F = 3.2, p < 0.04 for semitendinosus-vastus medialis). This could predispose these muscles to over strain and possible injuries. The main effect of fatigue condition and its interaction with velocity however, showed statistically nonsignificant result.