Critical power: a paradigm-shift for benchmarking exercise testing and prescription.

Abstract

Inherent in the work of Collins et al. (2022) is the notion that prescription of exercise intensity relative to CP (and also the gas exchange threshold, GET; see Lansley et al., 2011) will reduce the variability in physiological responses and exercise tolerance. And that is precisely the hypothesis tested by Meyler et al. (2023) in this issue of Experimental Physiology. Specifically, in healthy men and women who completed multiple exhausting cycling tests (graded exercise test, series of constant-power tests) to define GET, CP and W′, these parameters and also V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ (i.e., at defined percentages of V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ ) were utilized to anchor separate moderate- (MOD), heavy- and severe-intensity criterion exercise bouts. Subsequently, two series of MOD, HEAVY and SEVERE exercise bouts, the latter as high intensity 5 × 3 min intervals, were prescribed ‘traditionally’ (TRAD) based upon V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ (i.e., 50%, 77% and 85%) or using the GET and CP parameters (THR; MOD: 30 min at 90% GET; HEAVY: 20 min at 50%∆ (midway between GET and CP); and SEVERE: at 110% CP). Primary results supported the hypothesis for HEAVY and SEVERE exercise with respect to reduced variability of work rates for THR versus TRAD. Crucially, whereas some subjects for HEAVY–TRAD exercised in the severe-intensity domain with the attendant V ̇ O 2 ${\dot V_{{{\rm{O}}_2}}}$ and [lactate] consequences – and 70% of them became exhausted for TRAD versus 0% for THR – this was not the case for HEAVY–THR. For the SEVERE trials neither peak nor mean V ̇ O 2 ${\dot V_{{{\rm{O}}_2}}}$ and heart rate variability were different between TRAD and THR, but peak and mean [lactate] variability were lower for THR, as was percentage W′ depletion. The scientific literature is, unfortunately, replete with examples of otherwise very well designed studies where the investigators have chosen to ‘normalize’ heavy exercise intensity by exercising their participants at either a fixed % V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ , often 75% or 80%, or at 50%∆ between GET and V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ . So doing has resulted in highly divergent physiological responses characteristic of some participants exercising in the heavy (i.e., stable V ̇ O 2 ${\dot V_{{{\rm{O}}_2}}}$ and [lactate] profiles, Tlim >> 30 min) and others in the severe (i.e., V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ achieved, rising [lactate], exhaustion < 20 min) exercise domains. Meyler et al. (2023) demonstrate that prescribing exercise relative to CP can prevent this occurrence and, even for supra-CP exercise, reduce inter-subject response variability for key physiological indices. This rationale has also been presented, on a more theoretical level, for normalizing the assessment of exercise for therapeutic efficacy across patient populations, especially chronic obstructive pulmonary disease (Whipp & Ward, 2009). Although beyond the limits of the measurements in Meyler et al. (2023), it is also important to note that, by registering severe-intensity exercise bouts to CP and thereby lowering inter-subject variability for W′ depletion, it would be expected that greater homogeneity would be achieved across participants for intramyocyte perturbations (e.g., ∆[PCr], [Pi], [ADPfree], [H+], [glycogen]; Jones et al., 2008) in addition to, of course, improved ability to predict exercise tolerance. The implications and therefore putative impact of the findings of Meyler et al. (2023) are substantial and reach across the preserves of exercise science to better inform, prescribe and evaluate athletic training regimens, improve the assessment of the efficacy of therapeutic interventions and, of course, help resolve the mechanistic bases for exercise intolerance itself. Both authors have read and approved the final version of this manuscript and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed. None declared. None.