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Fatigue reduces the complexity of knee extensor torque during fatiguing sustained isometric contractions

Pethick, Jamie, Winter, Samantha L., Burnley, Mark (2019) Fatigue reduces the complexity of knee extensor torque during fatiguing sustained isometric contractions. European Journal of Sport Science, 19 (10). pp. 1349-1358. ISSN 1746-1391. (doi:10.1080/17461391.2019.1599450) (KAR id:73956)


The temporal structure, or complexity, of muscle torque output reflects the adaptability of motor control to changes in task demands. This complexity is reduced by neuromuscular fatigue during intermittent isometric contractions. We tested the hypothesis that sustained fatiguing isometric contractions would result in a similar loss of complexity. To that end, nine healthy participants performed, on separate days, sustained isometric contractions of the knee extensors at 20% MVC to task failure and at 100% MVC for 60 s. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling were quantified by calculating approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Global, central and peripheral fatigue were quantified using maximal voluntary contractions (MVCs) with femoral nerve stimulation. Fatigue reduced the complexity of both submaximal (ApEn from 1.02 ± 0.06 to 0.41 ± 0.04, P < 0.05) and maximal contractions (ApEn from 0.34 ± 0.05 to 0.26 ± 0.04, P < 0.05; DFA α from 1.41 ± 0.04 to 1.52 ± 0.03, P < 0.05). The losses of complexity were accompanied by significant global, central and peripheral fatigue (all P < 0.05). These results demonstrate that a fatigue-induced loss of torque complexity is evident not only during fatiguing intermittent isometric contractions, but also during sustained fatiguing contractions.

Item Type: Article
DOI/Identification number: 10.1080/17461391.2019.1599450
Uncontrolled keywords: Muscle, neuromuscular fatigue, non-linear dynamics, complexity, fractal scaling
Subjects: G Geography. Anthropology. Recreation > GV Recreation. Leisure > Sports sciences
Divisions: Divisions > Division of Natural Sciences > Sport and Exercise Sciences
Depositing User: Mark Burnley
Date Deposited: 17 May 2019 14:01 UTC
Last Modified: 28 Jul 2022 22:10 UTC
Resource URI: (The current URI for this page, for reference purposes)

University of Kent Author Information

Pethick, Jamie.

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Winter, Samantha L..

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Burnley, Mark.

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