Wavelet analysis of the m. vastus lateralis surface electromyogram activity in incremental tests until exhaustion using bicycle and knee extension exercises

Continuous wavelet analysis was used to study the spectral characteristics of the m. vastus lateralis electromyographic activity in two I : rhythmic knee-joint extensions and cycling. Wavelet analysis of surface electromyograms (EMGs) recorded during cyclic contractions of the same muscle during the two types of movements showed differences in the pattern of changes in the timefrequency characteristics of the signal during a single cycle of movements with different loads, as well as differences in the slow variations of spectral characteristics related to the development of muscle fatigue during the tests. It was shown that, during cycling at low loads (the beginning of the test) the EMG activity peaked during the second half of the muscle contraction (the angle in the knee joint was ≈140°); the increase in the 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 the muscle contraction remained almost unchanged. During knee-joint extension, the maximum EMG activity was observed at the very end of the active phase of movement for all loads, and the median frequency significantly increased with increasing angle at the knee joint. The long-term time course of the EMG intensity growth during these tests also differed, whereas the changes in the wavelet-spectrum median frequencies were practically the same: they increased during both tests.