Variability in exercise tolerance and physiological responses to exercise prescribed relative to physiological thresholds and to maximum oxygen uptake

Abstract

The objective of this study was to determine whether the variability in exercise tolerance and physiological responses is lower when exercise is prescribed relative to physiological thresholds (THR) compared to traditional intensity anchors (TRAD).Ten individuals completed a series of maximal exercise tests and a series of moderate (MOD), heavy (HVY) and severe intensity (HIIT) exercise bouts prescribed using THR intensity anchors (critical power and gas exchange threshold) and TRAD intensity anchors (maximum oxygen uptake; VO 2 max ). There were no differences in exercise tolerance or acute response variability between MOD THR and MOD TRAD . All individuals completed HVY THR but only 30% completed HVY TRAD . Compared to HVY THR , where work rates were all below critical power, work rates in HVY TRAD exceeded critical power in 70% of individuals. There was, however, no difference in acute response variability between HVY THR and HVY TRAD . All individuals completed HIIT THR but only 20% completed HIIT TRAD . The variability in peak (F = 0.274) and average (F = 0.318) blood lactate responses was lower in HIIT THR compared to HIIT TRAD . The variability in W′ depletion (the finite work capacity above critical power) after the final interval bout was lower in HIIT THR compared to HIIT TRAD (F = 0.305). Using physiological thresholds to prescribe exercise intensity reduced the heterogeneity in exercise tolerance and physiological responses to exercise spanning the boundary between the heavy and severe intensity domains. To increase the precision of exercise intensity prescription, it is recommended that, where possible, physiological thresholds are used in place of VO 2 max . K E Y W O R D Scritical power, exercise intensity, exercise prescription, interindividual differences INTRODUCTIONCardiorespiratory fitness, measured as maximum oxygen uptake ( VO 2 max ), is an important marker of both endurance performanceThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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

“…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 $${\dot V_{{{\rm{O}}_2}\max }}$$ (i.e., at defined percentages of $${\dot V_{{{\rm{O}}_2}\max }}$$) were utilized to anchor separate moderate‐ (MOD), heavy‐ and severe‐intensity criterion exercise bouts.…”

Critical power is a key threshold determining the magnitude of post‐exercise hypotension in non‐hypertensive young males

“…However, these previous studies examining the effect of exercise intensity on post‐exercise hypotension prescribed exercise as a percentage of $${\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}{\mathrm{max}}}$$ or maximal heart rate, rather than using a threshold‐based approach, as in the present study. Due to inter‐individual variation in the occurrence of the lactate threshold (approximated herein as the GET) and critical power relative to $${\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}{\mathrm{max}}}$$, exercise prescribed at a fixed percentage of $${\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}{\mathrm{max}}}$$ can result in some subjects performing exercise below their lactate threshold or critical power, and some subjects above these thresholds (Iannetta et al., 2020; Lansley et al., 2011; Meyler et al., 2023). Hence, if the goal is to determine the influence of exercise intensity on a given variable, normalizing exercise intensity as a fraction of $${\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}{\mathrm{max}}}$$ will result in increased inter‐individual variability in the physiological responses to exercise, which will cloud the ability of the researchers to observe the true effect of a given variable, should the effect exist.…”

“…As the physiological responses to exercise differ so markedly between each domain, there is the possibility that the failure of previous studies to find an effect of exercise intensity on the magnitude of post-exercise hypotension was due to those studies not appropriately accounting for metabolic thresholds, which occur at highly variable fractions of VO 2 max between individuals (Iannetta et al (2020(Iannetta et al ( , 2021; recently highlighted in this journal by Meyler et al (2023) and Poole and Jones (2023)). Exercise performed above critical power results in a greater post-exercise increase in vascular conductance when compared to sub-critical power exercise (Hammer et al, 2021), and post-exercise changes in vascular conductance are closely linked to the occurrence of post-exercise hypotension (Halliwill et al, 1996(Halliwill et al, , 2000.…”

Our understanding of the role of exercise intensity can only be precise as our classification of exercise intensity

“…Recognition of these shortcomings has led several researchers to recommend classifying exercise intensity in relation to physiological thresholds, like LT and CP (Collins et al, 2022;Meyler et al, 2023). Indeed, prescribing the intensity of exercise in relation to CP has been shown to produce more homogeneous responses to exercise (Meyler et al, 2023;Poole et al, 2016) and more predictable adaptations (Collins et al, 2022) In conclusion, the results of Lei et al's study and several other recent studies (Collins et al, 2022;Meyler et al, 2023;Poole et al, 2016) show that the seemingly random responses to traditionally prescribed exercise can often be explained, at least in part, when intensity is considered in relation to physiological thresholds. Future studies should consider classifying exercise based on physiological thresholds, like CP, rather than arbitrarily selected percentages of VO 2 max or HR max .…”

“…Third, it should be acknowledged that having subjects exercise at a fixed percentage of $${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$$ or HR max does not guarantee that similar cardiometabolic conditions are experienced by each subject. The cardiometabolic strain of exercise pivots around physiological thresholds, like LT and CP, which do not occur at the same %$${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$$ or %HR max for everyone (Collins et al., 2022; Meyler et al., 2023; Poole et al., 2016). Consequently, the power output associated with a fixed %$${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$$ (e.g., 70% $${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$$) during a graded exercise test could be above CP for one person and below CP for another, which could result in wildly different levels of cardiometabolic strain for each person (Meyler et al., 2023).…”