ENDURANCE EXERCISE TRAINING IS ASSOCIATED WITH ELEVATED BASAL SYMPATHETIC-NERVE ACTIVITY IN HEALTHY OLDER HUMANS

We tested the hypothesis that endurance training is associated with al tered basal levels of muscle sympathetic nerve activity (MSNA) and res ponses to acute stress in healthy older adults. MSNA (peroneal microne urography) and plasma norepinephrine (NE) concentrations were measured during supine rest, a cold presser test, and isometric handgrip (40% maximal voluntary force to exhaustion) in 16 older masters endurance a thletes [10 men, 6 women; 66 +/- 1 (SE) yr] and 15 healthy normotensiv e untrained control subjects (9 men, 6 women; 65 +/- 1 yr). The athlet es had higher levels of estimated daily energy expenditure and maximal oxygen uptake and lower levels of resting heart rate and body fat tha n the control subjects (all P < 0.05). MSNA during supine rest was ele vated in the athletes whether expressed as burst frequency (43 +/- 2 v s. 32 +/- 3 bursts/min, respectively; P < 0.05) or burst incidence (75 +/- 4 vs. 52 +/- 5 bursts/100 heartbeats, respectively; P < 0.01). Th ese whole group differences were due primarily to markedly higher leve ls of MSNA in the athletic vs. untrained women (48 +/- 4 vs. 25 +/- 3 bursts/min, 82 +/- 3 vs. 38 +/- 3 bursts/100 heartbeats, respectively, P < 0.001). In contrast, basal plasma NE concentrations were not sign ificantly different in the athletes vs. control subjects. The MSNA and plasma NE responses to acute stress tended to be greater in the athle tes. These findings indicate that vigorous regular aerobic exercise is associated with an elevated level of MSNA at rest and a tendency for an enhanced response to acute stress in healthy normotensive older hum ans.