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

Abstract

New findings: What is the central question of this study? Does prescribing exercise intensity using physiological thresholds create a more homogeneous exercise stimulus than using traditional intensity anchors? What is the main finding and its importance? Prescribing exercise using physiological thresholds, notably critical power, reduced the variability in exercise tolerance and acute metabolic responses. At higher intensities, approaching or exceeding the transition from heavy to severe intensity exercise, the imprecision of using fixed % ${\dot{V}}_{O_2\max }$ as an intensity anchor becomes amplified.

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; ${\dot{V}}_{O_2\max }$ ). 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 ${\dot{V}}_{O_2\max }$ .

Keywords: critical power; exercise intensity; exercise prescription; interindividual differences.