VARIABILITY AND INTERRELATIONSHIPS OF SURFACE EMG PARAMETERS DURING LOCAL MUSCLE FATIGUE

The inter- and intraindividual variability of the frequency power dens ity spectral and surface EMG amplitude parameters and of the muscle fi ber conduction velocity (MFCV) is studied in 26 healthy volunteers dur ing fatiguing isometric ischemic intermittent exercise of the m. bicep s brachii at 80% of the maximal voluntary contraction level, with a co ntraction rate of 30/min. No significant age effects were found. Males were significantly stronger compared with females. The higher initial SEMG amplitude and the stronger shift of the frequency power density spectrum (PDS) to lower frequencies appear to be significantly correla ted with males. Fatigue induces an almost proportional compression of the SEMG frequency content. The muscle fiber conduction velocity has t he highest intraindividual reproducibility (r = 0.81). Despite the def inite and strong influence of the MFCV on the PDS, the shift of the PD S can not be explained by a change of MFCV alone.