Development of fatigue during repeated eccentric-concentric muscle contractions of plantar flexors in patients with stroke

Abstract

Objective: To better understand the mechanisms behind fatigue in muscles affected by a neuromuscular disease. Design: Patients recruited by convenience compared to age-matched healthy subjects from a population study. Setting: University hospital laboratory. Methods: Repetitive eccentric-concentric plantar flexions at 60°/sec were performed on a dynamometer until exhaustion. The mean power frequency and root mean square of the electromyogram were recorded, and work was calculated. Subjects: Both legs of seven patients with upper motor neuron lesion from stroke and one leg of healthy men were tested. Results: There were no significant ( p > .05) differences in number of cycles performed or decrease of work between any of the tested legs. There was a significant ( p > .05) difference in work performed by the affected leg and the reference group. Mean power frequency decreased significantly ( p > .05) for the gastrocnemius muscle in the nonaffected leg and for the reference group, while no such decreases were found in the affected leg. The statistical methods used were the nonparametric tests: the Wilcoxon one-sample for differences between paired observations, and the Mann-Whitney U for differences between groups. Conclusion: A reduction in work in high-intensity dynamic muscle activity may not be associated with a reduction in mean power frequency, especially in patients with altered supraspinal control. There may be peripheral fatigue factors not reflected in the electromyographic activity.