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

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

 

Author: So, Chi-hung Raymond
Title: Fatigue of lower limb muscles during repetitive cycling exercise : electromyographic assessment and intervention
Degree: Ph.D.
Year: 2009
Subject: Hong Kong Polytechnic University -- Dissertations.
Cycling -- Physiological aspects.
Leg -- Muscles -- Mathematical models.
Wavelets (Mathematics)
Department: Dept. of Rehabilitation Sciences
Pages: 140 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2306837
URI: http://theses.lib.polyu.edu.hk/handle/200/3624
Abstract: Introduction 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. Experiment 1 As wavelet transform is possible to quantify temporal changes of the frequency content of surface EMG under dynamic condition without losing resolution in time or frequency, this study 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. Methods: Eleven active young males were tested for maximal isokinetic knee extension and flexion exercise for 50 repetitions at 180osec-1 and at a range of 100o-0o Surface EMG (sEMG) of vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) were recorded during the exercise. Wavelet transform was used to filter the sEMG data into 11 wavelet domains. The movement was divided into five 20o angle range groups. Results: The most significant and consistent trend of decrease in sEMG intensity power under maximal dynamic exercise for VM, VL and RF was identified at the angle range of 40o-20o in wavelet domain 4 which has a center frequency of 92.4 Hz and bandwidth of 35.2 Hz. Experiment 2 For revealing 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 maximal cycling exercise. Methods: Eight young male cyclists volunteered for this study. After warm up on a cycling ergometer, they ride at 95% of individual VO2max power at 90 rev min-1 for 5 minutes. Surface EMG (sEMG) data were recorded during the exercise from gluteus maximus, rectus femoris, vastus medialis, vastus lateralis, biceps femoris, semitendinosus, tibialis anterior and medial gastrocnemius. The sEMG data were then wavelet transformed. Cross-correlation was used to quantify the phase-shift or delay of the power intensity of the wavelet data in each pedaling cycle. Results: The medial gastrocnemius and rectus femoris had the longest delay in activities. The delay of activities of the biarticular muscles might be related to their duo function at different phases (recovery and propulsive) 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. Experiment 3 The aim of this study was to evaluate the effect of transcutaneous electrical acupoint stimulation (TEAS) at selected acupoints on enhancing the rate of muscle force recovery after strenuous knee extension/flexion exercise. Methods: Ten male and seven female healthy young adults participated in this study in which they performed isokinetic knee fatigue exercise on the Biodex System 3 ergometer. Subjects underwent 15 minutes of either TEAS or pseudo-TEAS recovery treatment after the isokinetic exercise on two separate days. The TEAS treatment was applied on 4 selected acupoints Zusanli (ST36), Chenshan (BL57), Yanglingquan (GB34) and Sanyinjiao (SP6)) while the pseudo-TEAS treatment was applied to the points away from the true acupoints. Results: The results indicated that the TEAS treatment was significantly more effective than the pseudo-TEAS treatment in enhancing the rate of muscle force recovery. It is proposed that pain control is a plausible mechanism to explain the benefit of TEAS treatment. As TEAS is a non-invasive and simple treatment, it is feasible to apply it during and immediately after training. Conclusion Wavelet transform of the frequency content of the muscle surface EMG measured at exhaustive cycling exercise revealed that the subjects altered the pattern of muscle activation pattern during the exercise and the biarticular muscles were the most fatigue sensitive muscles. It was also found that TEAS treatment was effective in enhancing the rate of muscle recovery after fatigue induced exercise.

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