Changes in relations between surface electromyogram and fatigue level by repeating fatiguing static contractions.

Abstract

Changes in relations between surface electromyogram (EMG) and fatigue level estimated by fatigue sensation were studied during repeated fatiguing static contractions. Six male subjects performed elbow flexion of 13-15%MVC. Contractions were repeated 5 times (C1, C2, C3, C4, C5) with 5 min intervals of rests. The contractions continued until the onset of fatigue sensation such as obvious pain or considerable tiredness. Bipolar surface EMGs were recorded from 6 synergists of elbow flexors. Mean amplitude (AEMG) and relative power spectrum (RPW) of EMG were calculated. Partial correlation coefficients between time, AEMG, and RPW during each contraction were calculated. AEMG increased with time. EMG spectrum shifted towards lower frequencies with time. The correlations between AEMG and RPW were negative below 60Hz. AEMG and RPW were compared between C1 and C2-C5 being related with fatigue sensations. The changes in AEMG and EMG spectrum with the repeated contractions were similar to those with the development of fatigue. The increases in AEMG with the repeats were seen in most synergists in 4 subjects. Though EMG roughly reflected the fatigue during work, the changes of EMG were thought to include active adaptation to work.