Microneurographic characterization of sympathetic responses during 1-leg exercise in young and middle-aged humans

Muscle sympathetic nerve activity (MSNA) at rest increases with age. However, the influence of age on MSNA recorded during dynamic leg exercise is unknown. We tested the hypothesis that aging attenuates the sympatho-inhibitory response observed in young subjects performing mild to moderate 1-leg cyc...

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Published in:	Applied physiology, nutrition, and metabolism nutrition, and metabolism, 2019-02, Vol.44 (2), p.194-199
Main Authors:	Notarius, Catherine F, Millar, Philip J, Doherty, Connor J, Incognito, Anthony V, Haruki, Nobuhiko, O’Donnell, Emma, Floras, John S
Format:	Article
Language:	eng
Subjects:	Adolescent Adult Aged aging Aging (Biology) Aging - physiology Anaerobic Threshold Bicycling - physiology Blood pressure Blood Pressure - physiology Cycling dynamic exercise exercice dynamique Exercise Exercise - physiology Female Heart rate Humans Hypotheses Leg muscles Male Maximum oxygen consumption microneurographie microneurography Middle age Middle Aged Muscle, Skeletal - innervation Muscle, Skeletal - physiology Neuromuscular transmission Oxygen Consumption - physiology Physiological aspects Physiological research Sympathetic nervous system Sympathetic Nervous System - physiology vieillissement Young Adult Young adults
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Summary:	Muscle sympathetic nerve activity (MSNA) at rest increases with age. However, the influence of age on MSNA recorded during dynamic leg exercise is unknown. We tested the hypothesis that aging attenuates the sympatho-inhibitory response observed in young subjects performing mild to moderate 1-leg cycling. After predetermining peak oxygen uptake, we compared contra-lateral fibular nerve MSNA during 2 min each of mild (unloaded) and moderate (30%–40% of the work rate at peak oxygen uptake, halved for single leg) 1-leg cycling in 18 young (age, 23 ± 1 years (mean ± SE)) and 18 middle-aged (age, 57 ± 2 years) sex-matched healthy subjects. Mean height, weight, resting heart rate, systolic blood pressure, and percent predicted peak oxygen uptake were similar between groups. Middle-aged subjects had higher resting MSNA burst frequency and incidence (P < 0.001) and diastolic blood pressure (P = 0.04). During moderate 1-leg cycling, older subjects’ systolic blood pressure increased more (+21 ± 5 vs. +10 ± 1 mm Hg; P = 0.02) and their fall in MSNA burst incidence was amplified (−19 ± 2 vs. −11 ± 2 bursts/100 heart beats; P = 0.01) but because heart rate rose less (+15 ± 3 vs. +19 ± 2 bpm; P = 0.03), exercise induced similar reductions in burst frequency (P = 0.25). Contrary to our initial hypothesis, with advancing age, mild- to moderate-intensity dynamic leg exercise elicits a greater rise in systolic blood pressure and a larger fall in MSNA.
ISSN:	1715-5312 1715-5320