[Wavelet analysis of m. vastus lateralis surface EMG activity in incremental tests till exhaustion using bicycle and...

Continuous wavelet analyses was applied to investigate the spectral characteristics of m. vastus lateralis EMG activity in two incremental tests till exhaustion: rhythmic knee-joint extensions and cycling. Wavelet analysis of surface EMG revealed differences in the dynamics of time-frequency characteristics of the signal during single cycle of two types of movements with different loads, as well as differences in the slow variations of spectral characteristics associated with the development of muscle fatigue during the tests. It was shown that during cycling with low loads (beginning of the test) maximum of EMG activity was confined within the second half of muscle contraction (the angle in the knee joint approximately 140 degrees), increase of load at the end of the test led to a shift of the peak to the beginning of the active phase of movement, while the median frequency of the "instant" wavelet spectra during muscle contraction remained almost unchanged. During knee-joint extensions the maximum of EMG activity was observed at the end of the active phase of movement for all loads, median frequency increased significantly with increasing the angle at the knee joint. Long-term dynamics of EMG intensity growth during these tests differed as well, whereas dynamics of wavelet-spectra median frequencies were practically the same--during both tests their growths were observed.