Upward resetting of the vascular sympathetic baroreflex in middle-aged male runners

Abstract

This study focussed on the influence of habitual endurance exercise training (i.e. committed runner or non-runner) on the regulation of muscle sympathetic nerve activity (MSNA) and arterial pressure in middle-aged (50 to 63 years, n= 23) and younger (19 to 30 years; n=23) normotensive men. Haemodynamic and neurophysiological assessments were performed at rest. Indices of vascular sympathetic baroreflex function were determined from the relationship between spontaneous changes in diastolic blood pressure (DBP) and MSNA. Large vessel arterial stiffness and left ventricular stroke volume also were measured. Paired comparisons were performed within each age-category. Mean arterial pressure and basal MSNA bursts·min-1 were not different between age-matched runners and non-runners. However, MSNA bursts·100 heartbeats-1, an index of baroreflex regulation of MSNA (vascular sympathetic baroreflex operating point) was higher for middle-aged runners (P=0.006), whereas this was not different between young runners and non-runners. The slope of the DBP-MSNA relationship (vascular sympathetic baroreflex gain) was not different between groups in either age-category. Aortic pulse wave velocity was lower for runners of both age-categories (P<0.03), although carotid β stiffness was lower only for middle-aged runners (P=0.04). For runners of both age-categories, stroke volume was larger, while heart rate was lower (both P<0.01). In conclusion, we suggest that neural remodelling and upward setting of the vascular sympathetic baroreflex compensates for cardiovascular adaptations after many years committed to endurance exercise training, presumably to maintain arterial blood pressure stability.