Utility of EMG Indices in Evaluating Rectus Femoris Muscle Fatigue Induced by Intermittent Sprinting Cycling Exercise Based on Grey Association Analysis

Objective:To compare the utility of EMG indices in assessing rectus femoris muscle fatigue induced by intermittent sprinting cycling exercise based on grey association analysis,therefore to determine the optimal method to evaluating muscle fatigue. Methods:Ten cyclists performed five intermittent exercise bouts with 6-second all-out cycling exercise protocol,a recovery phase with 24-second low intensity cycling was set between every two bouts. The power output, cadence and surface electromyography(sEMG)of the right rectus femoris muscle were measured. Combined with time-domain,fourier transform,wavelet packet transformation and nonlinear analysis method,the RMS,MF,MPF,MDF,MNF,C(n),FD(Fractal Dimension)and SE(Sample Entropy)of sEMG were calculated. Results:The power output and cadence were decreased progressively with the increase of cycling phase and time duration. The MNF and SE showed the same change tendency with power output and cadence.The grey association grade between SE and exercise performance(power output and cadence)was significantly higher than the other sEMG indices,and the next parameter was the MNF. However,the FD parameter have the lowest correlation. Results:During intermittent sprinting cycling exercise,the rapid high intensity workload contraction with interval recovery will induce severe peripheral fatigue in rectus femoris muscle. The EMG indices of SE which is calculated based on nonlinear analysis is the optimal parameter in evaluating rectus femoris muscle fatigue induced by intermittent sprinting cycling exercise.