Local muscle fatigue in repetitive work.

Abstract

Severe local muscle fatigue may be a precursor of repetition strain injuries (RSI). In any event it produces discomfort and limits production. This fatigue is evaluated by analysing the amplitude and frequency of the electromyographic signals of the extensor and flexor muscles during repetitive wrist extension against a constant torque. The absolute integral of the signal increased with extension angle but did not change with the exercise time period. This suggests that amplitude analysis is better for the evaluation of load, and frequency analysis is better in evaluating fatigue. The rate of decrease of the centre frequency with exercise time was also higher for the higher extension angle, and it was higher for female than for male subjects. Ulnar deviation did not affect the rate of fatigue in these experiments. The methodology used here shows promise for the evaluation of tool, job and layout design to prevent RSI.