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Effect of muscle metaboreflex activation on spontaneous cardiac baroreflex sensitivity during exercise in humans

The present study sought to examine the hypothesis that muscle metaboreflex activation during exercise decreases spontaneous cardiac baroreflex sensitivity (cBRS) in humans. In protocol 1, nine male subjects (23±2 years) performed steady‐state leg cycling at low (90 bpm) and moderate (120 bpm) workloads, under free flow conditions and with muscle metaboreflex activation induced by bilateral thigh cuff inflation at 100 mmHg. In protocol 2, rhythmic handgrip exercise at 35% maximum voluntary contraction was performed with progressive upper arm cuff inflation (0, 80, 100 and 120 mmHg) to elicit graded metaboreflex activation. Heart rate (HR; ECG) and blood pressure (BP; Portapress) were continuously monitored and cBRS estimated using the sequence technique. Exercise‐induced increases in HR and BP during leg cycling were augmented with metaboreflex activation (P<0.01). However, exercise‐induced decreases in cBRS (18±2, 6±1, 3±2 ms/mmHg at rest, low and moderate exercise; P<0.01) were not affected by muscle metaboreflex activation. HR and BP also increased during rhythmic handgrip, and were further increased with graded metaboreflex activation. However, cBRS was unchanged throughout. In summary, these preliminary data suggest that the activation of the muscle metaboreflex during leg cycling or rhythmic handgrip exercise does not decrease cBRS in healthy young men.