Redefining Exhaustion: Considerations for the Modeling of Critical Power

Abstract

Background: The relationship between exercise intensity and the limit of tolerance is the focus of the Critical Power (CP) model. CP defines the upper limit for which exercise is steady state and is – in theory – indefinitely sustainable. However, this limit of tolerance at CP is often well below 30 min. Purpose: We want to test the hypothesis that 1) a clinically significant residual W’ capacity (W’res) does exist, 2) that the size of W’res is inversely related to tlim used in the testing protocols, and 3) that accounting for W’res will result in an improved calculation of the Critical Power (CP), as determined by an increased time to exhaustion at CP. Methods: Nine well-trained cyclists performed a ramp test and four high-intensity tests to exhaustion on a cycle ergometer to determine CP and the curvature constant (W’). Two tests to exhaustion were then performed at the traditional CP (CPtrad) and a novel, modified CP (CPmod) to test the practical significance of the residual capacity on the calculation of the CP. Results: All participants were able to perform work above CP even after reaching the limit of tolerance, despite no significant changes in physiological parameters. Including the W’res resulted in significantly lower estimations of CP (TRAD: 281W, MOD: 278 W; p = 0.015) and higher estimations of W’ (TRAD: 15.8 kJ, MOD: 17.8 kJ; p = 0.008). Significance: Athletes were able to continue generating power above CP, even after reaching the limit of tolerance. This residual capacity resulted in a significantly lower estimate of CP and significantly higher estimation of W’.