Cardiovascular reflex contributions to sympathetic inhibition during low intensity dynamic leg exercise in healthy middle‐age

Abstract

Aging augments resting muscle sympathetic nerve activity (MSNA) and sympatho‐inhibition during mild dynamic 1‐leg exercise. To elucidate which reflexes elicit exercise‐induced inhibition, we recruited 19 (9 men) healthy volunteers (mean age 56 ± 9 SD years), assessed their peak oxygen uptake (VO2peak), and, on another day, measured heart rate (HR), blood pressure (BP) and MSNA (microneurography) at rest and during 1‐leg cycling (2 min each at 0 load and 30%–40% VO2peak), 3 times: (1) seated +2 min of postexercise circulatory occlusion (PECO) (elicit muscle metaboreflex); (2) supine (stimulate cardiopulmonary baroreflexes);and (3) seated, breathing 32% oxygen (suppress peripheral chemoreceptor reflex). While seated, MSNA decreased similarly during mild and moderate exercise (p < 0.001) with no increase during PECO (p = 0.44). Supine posture lowered resting MSNA (main effect p = 0.01) BP and HR. MSNA fell further (p = 0.04) along with diastolic BP and HR during mild, not moderate, supine cycling. Hyperoxia attenuated resting (main effect p = 0.01), but not exercise MSNA. In healthy middle‐age, the cardiopulmonary baroreflex and arterial chemoreflex modulate resting MSNA, but contrary to previous observations in young subjects, without counter‐regulatory offset by the sympatho‐excitatory metaboreflex, resulting in an augmented sympatho‐inhibitory response to mild dynamic leg exercise.