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Loss of knee extensor torque complexity during fatiguing isometric muscle contractions occurs exclusively above the critical torque.

Pethick, Jamie and Winter, Samantha L and Burnley, Mark (2016) 'Loss of knee extensor torque complexity during fatiguing isometric muscle contractions occurs exclusively above the critical torque.' American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, 310 (11). R1144 - R1153. ISSN 0363-6119

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Abstract

The complexity of knee extensor torque time series decreases during fatiguing isometric muscle contractions. We hypothesized that because of peripheral fatigue, this loss of torque complexity would occur exclusively during contractions above the critical torque (CT). Nine healthy participants performed isometric knee extension exercise (6 s of contraction, 4 s of rest) on six occasions for 30 min or to task failure, whichever occurred sooner. Four trials were performed above CT (trials S1-S4, S1 being the lowest intensity), and two were performed below CT (at 50% and 90% of CT). Global, central, and peripheral fatigue were quantified using maximal voluntary contractions (MVCs) with femoral nerve stimulation. The complexity of torque output was determined using approximate entropy (ApEn) and the detrended fluctuation analysis-α scaling exponent (DFA-α). The MVC torque was reduced in trials below CT [by 19 ± 4% (means ± SE) in 90%CT], but complexity did not decrease [ApEn for 90%CT: from 0.82 ± 0.03 to 0.75 ± 0.06, 95% paired-samples confidence intervals (CIs), 95% CI = -0.23, 0.10; DFA-α from 1.36 ± 0.01 to 1.32 ± 0.03, 95% CI -0.12, 0.04]. Above CT, substantial reductions in MVC torque occurred (of 49 ± 8% in S1), and torque complexity was reduced (ApEn for S1: from 0.67 ± 0.06 to 0.14 ± 0.01, 95% CI = -0.72, -0.33; DFA-α from 1.38 ± 0.03 to 1.58 ± 0.01, 95% CI 0.12, 0.29). Thus, in these experiments, the fatigue-induced loss of torque complexity occurred exclusively during contractions performed above the CT.

Item Type: Article
Uncontrolled Keywords: Muscle, Skeletal, Knee Joint, Humans, Adaptation, Physiological, Muscle Fatigue, Physical Endurance, Isometric Contraction, Stress, Mechanical, Torque, Adult, Female, Male, Muscle Strength, Physical Exertion
Divisions: Faculty of Science and Health > Sport, Rehabilitation and Exercise Sciences, School of
Depositing User: Elements
Date Deposited: 03 Mar 2021 13:32
Last Modified: 03 Mar 2021 13:32
URI: http://repository.essex.ac.uk/id/eprint/29993

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