W′ expenditure and reconstitution during severe intensity constant power exercise: mechanistic insight into the determinants of W′

Ryan M Broxterman,Jesse C Craig,Thomas J Barstow,Phillip F Skiba,Carl J Ade,Samuel L Wilcox

doi:10.14814/phy2.12856

Ryan M Broxterman, Jesse C Craig + Show 4 more

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https://doi.org/10.14814/phy2.12856

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Abstract

The sustainable duration of severe intensity exercise is well‐predicted by critical power (CP) and the curvature constant (W′). The development of the W′BAL model allows for the pattern of W′ expenditure and reconstitution to be characterized and this model has been applied to intermittent exercise protocols. The purpose of this investigation was to assess the influence of relaxation phase duration and exercise intensity on W′ reconstitution during dynamic constant power severe intensity exercise. Six men (24.6 ± 0.9 years, height: 173.5 ± 1.9 cm, body mass: 78.9 ± 5.6 kg) performed severe intensity dynamic handgrip exercise to task failure using 50% and 20% duty cycles. The W′BAL model was fit to each exercise test and the time constant for W′ reconstitution (τ W′) was determined. The τ W′ was significantly longer for the 50% duty cycle (1640 ± 262 sec) than the 20% duty cycle (863 ± 84 sec, P = 0.02). Additionally, the relationship between τ W′ and CP was well described as an exponential decay (r 2 = 0.90, P < 0.0001). In conclusion, the W′BAL model is able to characterize the expenditure and reconstitution of W′ across the contraction–relaxation cycles comprising severe intensity constant power handgrip exercise. Moreover, the reconstitution of W′ during constant power severe intensity exercise is influenced by the relative exercise intensity, the duration of relaxation between contractions, and CP.

Highlights

The relationship between power output and exercise tolerance within the severe intensity exercise domain is well described by a hyperbolic equation, establishing the critical power (CP) and the curvature constant (W0) (Monod and Scherrer 1965; Whipp et al 1982; Poole 2008): t 1⁄4 ðP W0 À CPÞ (1)where t is the duration of exercise and P is the power output
The 20% duty cycle Ppeak (7.4 Æ 0.2 W) and CP (5.3 Æ 0.2 W) were significantly greater than the 50% duty cycle Ppeak (6.2 Æ 0.2 W, P < 0.001) and CP (4.1 Æ 0.2 W, P < 0.001), whereas W0 was not significantly different between the 20% duty cycle (479 Æ 45 J) and the 50% duty cycle (477 Æ 56 J, P = 0.95)
The average sW0 was significantly longer for the 50% duty cycle (1772 Æ 228 sec) than the 20% duty cycle (933 Æ 71 sec, P = 0.03)

Summary

Introduction

The relationship between power output and exercise tolerance within the severe intensity exercise domain is well described by a hyperbolic equation, establishing the critical power (CP) and the curvature constant (W0) (Monod and Scherrer 1965; Whipp et al 1982; Poole 2008): t 1⁄4 ðP W0 À CPÞ (1)where t is the duration of exercise and P is the power output. The relationship between power output and exercise tolerance within the severe intensity exercise domain is well described by a hyperbolic equation, establishing the critical power (CP) and the curvature constant (W0) (Monod and Scherrer 1965; Whipp et al 1982; Poole 2008): t 1⁄4 ðP W0 À CPÞ (1). W0 is the curvature constant of the power-duration relationship and represents a finite capacity for exercise performed above CP, for which task failure ensues with the complete expenditure of W0 (Monod and Scherrer 1965; Miura et al 1999, 2000; Coats et al 2003; Fukuba et al 2003; Ferguson et al 2007)

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