Critical Power

Abstract

The hyperbolic form of the power-duration relationship is rigorous and highly conserved across species, forms of exercise and individual muscles/muscle groups. For modalities such as cycling, the relationship resolves to two parameters, the asymptote for power (critical power, CP) and the so-called W′ (work doable above CP), which together predict the tolerable duration of exercise above CP. Crucially, the CP concept integrates sentinel physiological profiles - respiratory, metabolic and contractile - within a coherent framework that has great scientific and practical utility. Rather than calibrating equivalent exercise intensities relative to metabolically distant parameters such as the lactate threshold or V̇O2 max, setting the exercise intensity relative to CP unifies the profile of systemic and intramuscular responses and, if greater than CP, predicts the tolerable duration of exercise until W′ is expended, V̇O2 max is attained, and intolerance is manifested. CP may be regarded as a ‘fatigue threshold’ in the sense that it separates exercise intensity domains within which the physiological responses to exercise can (<CP) or cannot (>CP) be stabilized. The CP concept therefore enables important insights into 1) the principal loci of fatigue development (central vs. peripheral) at different intensities of exercise, and 2) mechanisms of cardiovascular and metabolic control and their modulation by factors such as O2 delivery. Practically, the CP concept has great potential application in optimizing athletic training programs and performance as well as improving the life quality for individuals enduring chronic disease.

The magnitude of neuromuscular fatigue is not intensity dependent when cycling above critical power but relates to aerobic and anaerobic capacities

“…The CP concept constitutes a potent framework for the investigation of exercise tolerance in the severe-intensity domain Grassi, Rossiter, & Zoladz, 2015;Murgatroyd, Ferguson, Ward, Whipp, & Rossiter, 2011;Poole, Burnley, Vanhatalo, Rossiter, & Jones, 2016). Its integration with electromyographic and mechanical measures of neuromuscular fatigue offers great potential for a better understanding of the limits of tolerance within the severe-intensity domain (Burnley et al, 2012).…”

Prediction of Critical Power and W′ in Hypoxia: Application to Work-Balance Modelling

“…The achievement of steady-state $\dot{\text{V}}$O 2 kinetics indicates the net energetic demand of the task can be met by oxidative metabolism (Poole et al, 2016). When the task requirement increases beyond CP the additional energetic demand is supplemented by substrate level phosphorylation (Vanhatalo et al, 2016) which induces non-steady state $\dot{\text{V}}$O 2 kinetics, accelerated degradation of high energy phosphates, and accumulation of metabolites involved in peripheral muscle fatigue (Jones et al, 2008; Poole et al, 2016). Since the total amount of work accumulated above CP is terminated at the moment of task failure, the mechanisms leading to task failure itself also determine the value of W′.…”

Robot-assisted assessment of muscle strength

“…Mathematically, the force-duration relationship is described as being hyperbolic. When exercise tolerance is considered, the force-asymptote is called “critical force” (CF) [55]. Alongside with the peak force value and the curvature constant obtained during the same test, CF provides an index of critical neuromuscular fatigue threshold.…”

“…2). Under these test conditions, the end-test moment (which corresponds to CM) occurs at approximately 30% of maximal intended isometric moment, meaning that during the test the moment falls before reaching stable values at approximately 30% of maximal intended isometric moment [55, 56].

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