Fatigue of lower limb muscles during repetitive cycling exercise: Electromyographic assessment and intervention

In order to reveal the strategies of muscle recruitment or fatigue pattern during cycling and to explore a practical and effective method to enhance recovery after fatigue exercise, three experiments were conducted.;The first experiment aimed to determine a wavelet domain and a joint range that has the lowest variance and highest sensitivity to document the shift of the frequency intensity that relates to the decline of dynamic muscle power along the maximal isokinetic knee extension and flexion exercise. The results indicated that the most significant and consistent trend of decrease in sEMG intensity power for vastus medialis, vastus lateralis and rectus femoris was identified at the angle range of 40°-20° in wavelet domain 4 which has a center frequency of 92.4 Hz and bandwidth of 35.2 Hz.;The second experiment was to reveal the strategies of muscle recruitment and fatigue pattern during cycling. Wavelet analysis and cross-correlation methods were used to analyze the continuous sEMG recordings from the major lower limb muscles so as to monitor the alternation of activation period and level of activity of those muscles during a cycling exercise at 95% of individual VO2max, power. It was found that the medial gastrocnemius and rectus femoris had the longest delay in activities and these might be related to their duo function at different phases of cycling. The respective increase and decrease in power intensities of the rectus femoris and medial gastrocnemius revealed that rectus femoris was increasing the force output while the medial gastrocnemius was experiencing fatigue during the 5-minute cycling. The results suggested that the subjects alternated the pattern of muscle activation in order to minimize the muscle fatigue and the biarticular muscles were the most fatigue sensitive muscles.;In the third experiment, it was found that the transcutaneous electrical acupoint stimulation (TEAS) at Zusanli (ST36), Chenshan (BL57), Yanglingquan (GB34) and Sanyinjiao (SP6) was effective on enhancing the rate of muscle force recovery after strenuous knee extension/flexion exercise. It is proposed that pain control is a plausible mechanism to explain the benefit of TEAS treatment.