Muscle metaboreflex activation increases ventilation and heart rate during dynamic exercise in humans

Abstract

New findings: What is the central question of this study? Classically, the stimulation of thin-fibre skeletal muscle afferents, via the application of postexercise circulatory occlusion (PECO) at rest, fails to generate ventilatory responses. We used a new experimental protocol to examine whether the involvement of these metabosensitive afferents in ventilatory control can only be revealed during exercise, when other potentially synergistic inputs that increase central respiratory drive are activated. What is the main finding and its importance? We found that PECO of one leg augmented the ventilatory and heart rate responses to single-legged exercise of the contralateral leg, suggesting that metaboreceptive muscle afferents contribute to the control of the exercise hyperpnoea.

Abstract: Inhibition of thin-fibre skeletal muscle afferent neurotransmission attenuates ventilatory and cardiovascular responses to exercise. However, stimulation of muscle metaboreceptive afferents at rest, via postexercise circulatory occlusion (PECO), classically fails to generate increases in ventilation or heart rate. It is possible that the involvement of muscle afferent feedback in ventilatory control can only be revealed during exercise, when other potentially synergistic inputs that increase central respiratory drive are activated. Therefore, we assessed the cardiorespiratory responses to single-legged cycling exercise with or without PECO of the contralateral leg. Thirteen healthy participants performed left-legged cycling exercise (40 or 60 W) followed by either: (i) no PECO (Con trial); or (ii) PECO (PECO trial) of the left leg for 3 min. During this 3 min period, right-legged cycling exercise was performed at the same workload as the preceding left-legged exercise (40 or 60 W). During 60 W right-legged cycling, ventilation relative to baseline was significantly higher in the PECO versus Con trial (22.9 ± 2 versus 18.7 ± 1.8 l min^-1 ; P < 0.05), but there was no difference between the trials performed at 40 W. The change in heart rate was significantly greater during right-legged cycling in the PECO versus Con trial in the 40 (41.2 ± 4 versus 34.1 ± 3.1 beats min^-1 ; P < 0.05) and 60 W trials (49.7 ± 2.7 versus 43.4 ± 3.7 beats min^-1 ; P < 0.05). There were no differences in oxygen uptake, carbon dioxide production and ratings of perceived exertion between trials. These findings suggest that stimulation of muscle metaboreceptive afferents can drive increases in ventilation and heart rate during dynamic exercise.

Keywords: exercise; muscle afferent feedback; respiratory control.