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Fatigue-induced changes in knee-extensor torque complexity and muscle metabolic rate are dependent on joint angle

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journal contribution
posted on 12.08.2021, 12:54 by Jamie Pethick, Sam WinterSam Winter, Mark Burnley
Purpose Joint angle is a signifcant determinant of neuromuscular and metabolic function. We tested the hypothesis that previously reported correlations between knee-extensor torque complexity and metabolic rate (mVȮ 2) would be conserved at reduced joint angles (i.e. shorter muscle lengths).
Methods Eleven participants performed intermittent isometric knee-extensor contractions at 50% maximum voluntary torque for 30 min or until task failure (whichever occurred sooner) at joint angles of 30º, 60º and 90º of fexion (0º=extension). Torque and surface EMG were sampled continuously. Complexity and fractal scaling of torque were quantifed using approximate entropy (ApEn) and detrended fuctuation analysis (DFA) α. mVȮ 2 was determined using near-infrared spectroscopy.
Results Time to task failure/end increased as joint angle decreased (P<0.001). Over time, complexity decreased at 90º and 60º (decreased ApEn, increased DFA α, both P<0.001), but not 30º. mVȮ 2 increased at all joint angles (P<0.001), though the magnitude of this increase was lower at 30º compared to 60º and 90º (both P<0.01). There were signifcant correlations between torque complexity and mVȮ 2 at 90º (ApEn, r= −0.60, P=0.049) and 60º (ApEn, r= −0.64, P=0.035; DFA α, ρ=0.68, P=0.015).
Conclusion The lack of correlation between mVȮ 2 and complexity at 30º was likely due to low relative task demands, given the similar kinetics of mVȮ 2 and torque complexity. An inverse correlation between mVȮ 2 and knee-extensor torque complexity occurs during high-intensity contractions at intermediate, but not short, muscle lengths.

Funding

The Leverhulme Trust (RPG-2016-440)

History

School

  • Sport, Exercise and Health Sciences

Published in

European Journal of Applied Physiology

Publisher

Springer Science and Business Media LLC

Version

VoR (Version of Record)

Rights holder

© The authors

Publisher statement

This is an Open Access Article. It is published by Springer under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/

Acceptance date

25/07/2021

Publication date

2021-08-05

ISSN

1439-6319

eISSN

1439-6327

Language

en

Depositor

Dr Sam Winter . Deposit date: 11 August 2021