Subjective and Electromyographic Assessment of Isometric Muscle Contractions

Abstract

Forty male subjects were asked to pull either 25 per cent or 50 per cent of their maximal voluntary contraction on an isometric dynamometer handle. During the pull they were asked to rate the pain experienced in the muscles on a five-point scale. During the task the active muscle was continuously monitored by recording the EMG.

The results indicated that individuals are able to predict their maximal endurance when concentrating on a dominant stimulus of pressure and/or pain in a physical task. The EMG analyses indicated that a differentiation can be made between physiological and psychological aspects of fatigue. The point in time when the EMG significantly increased in amplitude is interpreted to be the time when, due to motor unit impairment, the active muscle is fatigued. Additional contraction time was proposed to result from increased cortical recruitment, the length of which was determined by motivational elements.