Physiological aspects of muscular fatigue
Gilai, A.
Harefuah 98(11-12): 485-488
1980
ISSN/ISBN: 0017-7768 PMID: 7203189 Document Number: 162861
The mechanism of isometric fatigue was studied in maintained voluntary contraction of the extensor digitorum communis (EDC) muscle of the human hand and in single muscle fibers isolated from the flexor digiti brevis of the frog Xenopus. During low frequency (1 pulse/s) repetitive stimulation of the single muscle fibers tension decreased monotonically to a low level, which is termed fatigue. For each twitch the rate of tension relaxation rate was measured. During fatigue the relaxation rate was 70% less than the control value (21 s-1), while the isometric tension amplitude decreased by 55%. The excitability of the muscle fiber membrane during fatigue was not altered appreciably, as demonstrated by the amplitude and shape of the action potential. Electromyographic recording fom the EDC during prolonged isometric contraction at constant tension demonstrated a 6-fold increase in the average voltage area of a spike potential. In the recording of the evoked muscle action potential induced by stimulating the radial nerve at the arm, there was a gradual reduction of the muscle potential amplitude as fatigue induced by sustained isometric contraction was approached. A possible myogenic mechanism of muscle fatigue is suggested.