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

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 %  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; ). There were no differences in exercise tolerance or acute response variability between MOD and MOD . All individuals completed HVY but only 30% completed HVY . Compared to HVY , where work rates were all below critical power, work rates in HVY exceeded critical power in 70% of individuals. There was, however, no difference in acute response variability between HVY and HVY . All individuals completed HIIT but only 20% completed HIIT . The variability in peak (F = 0.274) and average (F = 0.318) blood lactate responses was lower in HIIT compared to HIIT . The variability in W' depletion (the finite work capacity above critical power) after the final interval bout was lower in HIIT compared to HIIT (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 .