Reduction in Force Complexity Following Eccentric Exercise That Elicits Exercise-Induced Muscle Damage.

UNLABELLED: Unaccustomed eccentric exercise has been shown to lead to muscle damage. Previous research suggests that fatigue reduces the complexity of muscle force output. However, previous research has not investigated whether the force complexity response to fatigue is affected by eccentric exercise. Therefore, the purpose of the present study was to examine the effect of eccentric exercise and a subsequent fatiguing task on force variability and complexity. METHODS: Twelve individuals (six females) participated in the study. The participants performed eccentric exercise consisting of six sets of 10 repetitions of the knee extensors to elicit muscle damage. Before and 48 hr after eccentric exercise, the participants were assessed for maximal voluntary contraction and performed a sustained isometric time to task failure protocol at 25% of maximal voluntary contraction. Force variability was assessed in the first 10 s (Fresh) and last 10 s (End-Task) of the time to task failure via standard deviation, coefficient of variation, detrended fluctuation analysis, sample entropy, and multiscale sample entropy. RESULTS: Maximal voluntary contraction (532.67 ± 177.49 N vs. 448.54 ± 186.92 N, p < .001) and time to task failure (197.10 ± 44.81 s vs. 157.70 ± 62.52 s, p = .031) were reduced after eccentric exercise. There were no differences in force variability following eccentric exercise at either the Fresh or End-Task time points. Force complexity was reduced at both Fresh (detrended fluctuation analysis: 1.37 ± 0.18 vs. 1.47 ± 0.21; sample entropy: 0.88 ± 0.27 vs. 0.71 ± 0.027) and End-Task (sample entropy: 0.63 ± 0.17 vs. 0.53 ± 0.15), following eccentric exercise compared with the pre-eccentric exercise condition. CONCLUSIONS: Reductions in force complexity, but not force variability, were observed following eccentric exercise. These changes are thought to be due to changes in motor control strategies to compensate for damaged tissue.