Abstract
We examined the etiology of the electromyographic (EMG) spectral shift during dynamic fatigue. Nineteen subjects (mean ± SD age = 22.4 ± 1.6 years) performed 50 consecutive maximal concentric isokinetic contractions of dominant leg extensors. Surface EMG signals were detected from the vastus lateralis, rectus femoris, and vastus medialis during each contraction, processed with a wavelet analysis, and the resulting spectra were decomposed with a nonparametric spectral decomposition procedure. The results indicated that the decreases in EMG frequency during the 50 contractions were generally due to reductions in high-frequency power and increases in low-frequency power. In addition, the spectral shifts were most pronounced for the rectus femoris, followed by the vastus lateralis, and then the vastus medialis. The spectral decomposition procedure is much more sensitive for tracking dynamic fatigue than is EMG mean frequency or median frequency.
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