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Physiological Evidence That the Critical Torque Is a Phase Transition, Not a Threshold
Jamie Pethick1, Samantha L Winter, Mark Burnley
1Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Kent, UNITED KINGDOM.
Medicine and Science in Sports and Exercise
|May 6, 2020
Summary
The transition between heavy and severe exercise intensity domains is gradual, not a sudden threshold. Critical power (CP) or critical torque (CT) does not represent an abrupt shift in physiological responses during exercise.
Area of Science:
- Exercise Physiology
- Sports Science
- Human Performance
Background:
- Distinct physiological responses characterize heavy- and severe-intensity exercise domains.
- These domains are separated by critical power (CP) or critical torque (CT).
- The precise nature of the transition between these exercise intensity domains remains unclear.
Purpose of the Study:
- To test the hypothesis that critical power/torque (CT) represents a sudden threshold.
- To investigate if there is a gradual transition from heavy- to severe-intensity exercise behavior around CT.
- To determine if CT is an abrupt threshold or a more nuanced transition zone.
Main Methods:
- Twelve healthy participants completed exhaustive severe-intensity trials to determine CT.
- Participants also performed 30-min trials near CT (CT-2, CT-1, CT+1, CT+2).
- Muscle oxygen uptake, electromyography, torque variability, complexity, and maximal voluntary contractions were measured.
Main Results:
- Rates of change in fatigue variables and physiological measures were significantly faster in severe trials compared to CT-2.
- Individual analyses revealed variability, with some near-CT trials showing severe responses and vice versa.
- Maximal voluntary contraction torque decline was significantly greater in severe-intensity trials.
Conclusions:
- The transition between heavy- and severe-intensity exercise is gradual.
- Critical power/torque (CT) does not function as an absolute, sudden threshold.
- Physiological responses exhibit a continuum rather than an abrupt shift at CT.
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