Alteration in Muscle Fatigue Caused by Load-Type Differences during Isometric Flexion of Human Fingers

Abstract

We measured the endurance time and force and assessed the electromyograms of the flexor digitorum muscle and extensor digitorum muscle in response to 2 types of submaximal fatiguing. The 2 tasks involved isometric contraction of the proximal interphalangeal joint flexor muscles at 50% of the maximum voluntary contraction (MVC) force, which was achieved either by maintaining a constant force while pulling a force transducer (force task) or by supporting an equivalent load while maintaining a constant proximal interphalangeal joint angle (position task). Seven men performed the 2 tasks with their index, middle, and ring fingers. For all 3 fingers, the endurance time for the force task (79 ± 22, 93 ± 46, and 96 ± 56 s for the index, middle, and ring fingers, respectively) was shorter than the corresponding values for the position task (141 ± 105, 147 ± 82, and 212 ± 91 s). The rate of change in amplitude and mean power frequency in the electromyogram did not significantly differ across the 2 tasks. Physiological tremor was computed from the recorded force signal. The physiological tremor initially decreased during both tasks; however, the subsequent increase occurred earlier during the force task.