Differential control of respiratory frequency and tidal volume during high-intensity interval training

Abstract

Since respiratory frequency (f_R) has been proposed as a good marker of physical effort, furthering the understanding of how f_R is regulated during exercise is of great importance. We manipulated recovery intensity and exercise duration during high-intensity interval training (HIIT) to test the hypothesis that fast inputs (including central command) contribute more than metabolic stimuli to f_R regulation. Seven male cyclists performed an incremental test, a 10 min and a 20 min continuous time trial (TT) as preliminary tests. Subsequently, recovery intensity and exercise duration were manipulated during HIIT (30 s work and 30 s active recovery) by performing four 10 min and one 20 min trial (recovery intensities: 85%, 70%, 55% and 30% of the 10 min TT mean workload; 85% of the 20 min TT mean workload). The work intensity of the HIIT sessions was self-paced by participants to achieve the best performance possible. When manipulating recovery intensity, f_R, but not tidal volume (V_T), showed a fast response to the alternation of the work and recovery phases, proportional to the extent of workload variations. No association between f_R and gas exchange responses was observed. When manipulating exercise duration, f_R and Rating of Perceived Exertion (RPE) were dissociated from V_T, V̇CO₂ and V̇O₂ responses. Overall, RPE was strongly correlated with f_R (r = 0.87; P < 0.001) but not with V_T. These findings may reveal a differential control of f_R and V_T during HIIT, with fast inputs appearing to contribute more than metabolic stimuli to f_R regulation. Differentiating between f_R and V_T may help unravel the mechanisms underlying exercise hyperpnoea.

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