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Physiological Evidence that the Critical Torque Is a Phase Transition Not a Threshold

Pethick, Jamie, Winter, Samantha L., Burnley, Mark (2020) Physiological Evidence that the Critical Torque Is a Phase Transition Not a Threshold. Medicine and Science in Sports and Exercise, . ISSN 0195-9131. (doi:10.1249/MSS.0000000000002389) (KAR id:81293)


Introduction: Distinct physiological responses to exercise occur in the heavy and severe-intensity domains, which are separated by the critical power or critical torque (CT). However, how the transition between these intensity domains actually occurs is not known. We tested the hypothesis that CT is a sudden threshold, with no gradual transition from heavy- to severe-intensity behavior within the confidence limits associated with the CT.

Methods: Twelve healthy participants performed four exhaustive severe-intensity trials for the determination of CT, and four 30-minute trials in close proximity to CT (one or two standard errors above or below each participant’s CT estimate; CT–2, CT–1, CT+1, CT+2). Muscle O2 uptake (mV[Combining Dot Above]O2), rectified EMG and torque variability and complexity were monitored throughout each trial, and maximal voluntary contractions with femoral nerve stimulation were performed before and after each trial to determine central and peripheral fatigue responses.

Results: The rates of change in fatigue-related variables, mV[Combining Dot Above]O2, EMG amplitude and torque complexity were significantly faster in the severe trials compared to CT–2. For example, the fall in maximal voluntary contraction (MVC) torque was –1.5 ± 0.8 N.m.min-1 in CT–2 vs. –7.9 ± 2.5 N.m.min-1 in the lowest severe-intensity trial (S1; P < 0.05). Individual analyses showed a low frequency of severe responses even in the circa-CT trials ostensibly above the CT, but also the rare appearance of severe-intensity responses in all circa-CT trials.

Conclusion: These data demonstrate that the transition between heavy- and severe-intensity exercise occurs gradually rather than suddenly.

Item Type: Article
DOI/Identification number: 10.1249/MSS.0000000000002389
Divisions: Divisions > Division of Natural Sciences > Sport and Exercise Sciences
Depositing User: Mark Burnley
Date Deposited: 18 May 2020 10:45 UTC
Last Modified: 04 Mar 2024 18:35 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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