Physiological, Perceptual, and Neuromuscular Responses to V˙O2-Clamp Cycle Ergometry Exercise

Abstract

Recommendations for endurance exercise prescription are often based on percentages of heart rate (HR) or the volume of oxygen consumption (V˙O2) maximum or reserve that is extrapolated to a power output (P) or velocity. Previous work has demonstrated dissociations of the expected responses to exercise anchored to the critical heart rate (CHR) compared with the P associated with CHR. However, it is unclear if similar dissociations due to reductions in P to maintain the designated intensity would be present during exercise anchored to the V˙O2 associated with CHR (V˙O2CHR). The purpose of this study was to examine the patterns in physiological (V˙O2, HR, P, respiration rate [RR], muscle oxygen saturation [%SmO2]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP, MMG AMP], mean power frequency [EMG MPF, MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise at V˙O2CHR (V˙O2-clamp). On separate days, ten participants (age: 25 ± 4 yr) performed a graded exercise test and four constant P trials at 85–100% of peak P (PP) to derive CHR and V˙O2CHR. Responses were recorded during a trial to exhaustion at V˙O2CHR (32.86 ± 7.12 mL·kg−1·min−1; TLim = 31.31 ± 21.37 min) and normalized in 10% intervals of TLim to their respective values at PP. The one-way repeated-measures ANOVA with post hoc, Bonferroni-corrected, pairwise comparisons indicated differences (p < 0.001) from baseline for HR (mean ± SD %change = 8 ± 3%), RR (43 ± 38%), P (−15 ± 5%), EMG MPF (10 ± 8%), and RPE (65 ± 38%), but no differences (p = 0.077–0.955) for %SmO2 (−17 ± 53%), EMG AMP (−3 ± 16%), MMG AMP (40 ± 61%), and MMG MPF (1 ± 7%). The loss in performance observed during V˙O2-Clamp exercise may provide a quantification of the inefficiency associated with the V˙O2 slow component phenomenon. The neuromuscular responses suggested constant muscle excitation despite the reductions in P, but the metabolic and perceptual responses suggested a combination of feedforward and feedback mechanisms regulating TLim. Future studies should further examine responses to the V˙O2-Clamp exercise at a uniform threshold.