BACKGROUND: Recommendations for cardiorespiratory endurance (CE) exercise prescription are based on vigorous ratings of perceived exertion (RPE), percentages of maximal heart rate (HRmax) or volume of oxygen consumption (VO2max). These intensities are then extrapolated to a power output (P) or velocity. Previous work has demonstrated dissociations of the metabolic responses when exercise is anchored to a constant RPE (RPE-clamp) due to alterations in P to maintain the designated perceptual intensity. However, the specific metabolic responses during vigorous RPE-clamp exercise (RPE=14-17) are unclear, and it is unknown if the resulting responses are within the recommended range for improvements in CE (64-90% VO2max). This study examined the metabolic (VO2) and P responses to RPE-clamp exercise at RPE 14 (RPE14) and RPE 17 (RPE17). METHODS: Twenty-one participants (Age=22±3yrs; Height=175.0±9.5cm; Mass=73.7±16.1kg) performed a graded exercise test to determine VO2max and peak power output (PP), followed by trials to exhaustion, or up to 60 minutes, at RPE14 (time to exhaustion [TLim]=60.0±0.0min) and RPE17 (TLim=59.5±2.3min) on a cycle ergometer. VO2 and P were normalized to their respective values at PP at each 10% of TLim. RESULTS: The two-way repeated measures ANOVA indicated there were significant RPE by time interactions (p<0.05) for VO2 and P. Follow-up analyses and Bonferroni-corrected, pairwise comparisons indicated that RPE17 VO2 (65±8%VO2max[means±SD reflect responses across entire trial]) and P (52±12%PP) were greater than RPE14 (61±4%VO2max; 48±7%PP) from 0-20% and 90% TLim (p<0.001-0.022). In addition, VO2 peaked at 10% TLim for both RPE14 and RPE17, followed by significant decreases after 30% and 20% TLim, respectively. P significantly decreased after 10% TLim and plateaued after 50% TLim for both RPE14 and RPE17. Qualitatively, the VO2 at RPE14 and RPE17 were above the recommended prescription guidelines from 10-20% and 0-40% TLim, respectively. CONCLUSIONS: RPE-clamp exercise at RPE17, but not RPE14, elicited a vigorous VO2 intensity for at least 20 minutes, meeting the current guidelines for improvements in CE. However, the VO2 and P at RPE14 and RPE17 converged by the end of trial, which suggests afferent feedback and efferent feedforward inputs regulate exercise intensity at a theoretical sensory tolerance limit that should be considered by researchers and practitioners.

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