Differences of Surface Electromyography during Incremental Cycling Exercise in Hypoxia and Normoxia Using Wavelet Transform Analysis

Abstract

Previous studies indicated that there was a difference between hypoxia and normoxia for amplitude parameters of surface electromyography (EMG). However, there are few reports on frequency parameters of EMG because of limitations of traditional analytical methods. PURPOSE: The purpose of this study was to investigate the differences of surface electromyography during incremental cycling exercise in hypoxia and normoxia using wavelet transform analysis. METHODS: Subjects were fourteen active and healthy men. (mean±SD; age: 21.08 ± 1.50 years; height: 1.69 ± 0.06 m; weight: 60.16 ± 7.77 kg; maximal oxygen consumption: 51.11. ±9.54 ml / min / kg). The subjects performed incremental cycling exercise test to exhaustion in hypoxia (FIO2: 13.4%) and normoxia conditions (FIO2: 20.9%). EMG activities of vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF) and biceps femoris (BF) were recorded during cycling exercise test at a sampling rate of 2000 Hz. Integrated electromyogram (iEMG) and mean power frequency (MPF) for each exercise intensity were calculated from the EMG data. Contentious wavelet analysis was used to calculate MPF, and mother wavelet was set at morlet wavelet. The differences between exercise intensities and FIO2 conditions were compared using a two-way analysis of variance. The significance level was set at p< 0.05. RESULTS: iEMG of each muscle significantly increased with increasing exercise intensities (all: p < 0.01). However, there were no significant differences between FIO2 conditions for each muscle (VL: p = 0.37; VM: p = 0.49; RF: p = 0.37; BF: p = 0.64). MPF of VL significantly decreased with increasing exercise intensities (p < 0.01), and MPF in hypoxia was higher than that in normoxia (p < 0.01). MPF of VM significantly decreased with increasing exercise intensities (p<0.01), but there were no significant differences between FIO2 conditions (p = 0.37). In addition, there were no significant differences between exercise intensities (RF: p = 0.49; BF: p = 0.57) and FIO2 conditions (RF: p = 0.49; BF: p = 0.19) for RF and BF. CONCLUSION: The current results demonstrated that the change in MPF was different for each muscle, and MPF of VL in hypoxia was only higher than that in normoxia, and suggested hypoxia exposure affects neuromuscular activity agonist muscle during exercise.