Fatigue, H/Q ratios and muscle coactivation in recreational football players

The objective of this study was twofold: first to assess the effect of fatigue on two muscle strength ratios: the conventional ratio – H_{con}/Q_{con} and dynamic control ratio(DCR) – H_{ecc}/Q_{con} and second to assess the coactivation of hamstrings and quadriceps during isokinetic knee flexion/extension. Eight recreational football players (mean ± SD age: 22 ± 2.3 yr; body mass: 85 ± 3.30~kg) volunteered to participate in this study. Peak concentric and eccentric torque of the hamstrings and quadriceps were measured at 120°/s pre and post fatigue using an isokinetic dynamometer. The fatiguing protocol consisted of 50 maximal concentric knee flexion/extension repetitions. Using surface EMG, peak RMS of the biceps femoris and vastus lateralis were measured in order to calculate muscle coactivation during extension and flexion of the knee. Paired samples t-tests concluded that there was a significant increase in both the conventional ratio (0.75 vs. 1.02) and the DCR (0.88 vs. 1.08) following fatigue. A significant increase in hamstring coactivation during concentric quadriceps muscle actions following fatigue was also observed (18.6 vs. 21.3%. These data contribute to the literature aiding the future development of the DCR and its use in injury prevention and rehabilitation strategies.