Relation between EMG power spectrum shifts and muscle fibre action potential conduction velocity changes during local muscular fatigue in man
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Muscular fatigue was studied in the human m. biceps brachii by contracting the muscle as long as possible at 50% of maximum voluntary strength. For 8 subjects changes in the muscle fibre action potential conduction velocity could successfully be measured using the cross-correlation technique between two surface EMG signals. Shifts in the EMG power spectrum were quantified using the mean power frequency (MPF) of the EMG power spectral density function.
During fatigue the EMG power spectrum gradually shifted to lower frequencies. The mean value and standard deviation of the MPF value decreased from (115±20) Hz at the beginning of the experiment to (60±18) Hz at the end. For 4 of the 8 subjects the decrease in MPF value was accompanied by a substantial decrease in conduction velocity (mean decrease was 33% of the initial velocity value). For the other 4 subjects, despite the great MPF changes, there was hardly any change in conduction velocity (mean decrease was 3%).
The present study shows that great EMG power spectral shifts during muscular fatigue may occur without a concomitant change in muscle fibre action potential conduction velocity.
Key wordsMuscular fatigue Isometric contraction M. biceps brachii EMG power spectrum shift Muscle fibre action potential conduction velocity
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