Concurrent metaboreflex activation increases chronotropic and ventilatory responses to passive leg movement without sex-related differences

Abstract

Previous studies in animal models showed that exercise-induced metabolites accumulation may sensitize the mechanoreflex-induced response. The aim of this study was to assess whether the magnitude of the central hemodynamic and ventilatory adjustments evoked by isolated stimulation of the mechanoreceptors in humans are influenced by the prior accumulation of metabolic byproducts in the muscle. 10 males and 10 females performed two exercise bouts consisting of 5-min of intermittent isometric knee-extensions performed 10% above the previously determined critical force. Post-exercise, the subjects recovered for 5 min either with a suprasystolic circulatory occlusion applied to the exercised quadriceps (PECO) or under freely-perfused conditions (CON). Afterwards, 1-min of continuous passive leg movement was performed. Central hemodynamics, pulmonary data, and electromyography from exercising/passively-moved leg were recorded throughout the trial. Root mean square of successive differences (RMSSD, index of vagal tone) was also calculated. Δpeak responses of heart rate (ΔHR) and ventilation ( $$\Delta \dot{V}_{{\text{E}}}$$ Δ V ˙ E ) to passive leg movement were higher in PECO compared to CON (ΔHR: 6 ± 5 vs 2 ± 4 bpm, p = 0.01; 3.9 ± 3.4 vs 1.9 ± 1.7 L min −1 , p = 0.02). Δpeak of mean arterial pressure (ΔMAP) was significantly different between conditions (5 ± 3 vs − 3 ± 3 mmHg, p < 0.01). Changes in RMSSD with passive leg movement were different between PECO and CON ( p < 0.01), with a decrease only in the former (39 ± 18 to 32 ± 15 ms, p = 0.04). No difference was found in all the other measured variables between conditions ( p > 0.05). These findings suggest that mechanoreflex-mediated increases in HR and $$\dot{V}_{{\text{E}}}$$ V ˙ E are sensitized by metabolites accumulation. These responses were not influenced by biological sex.

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