After-exercise heart rate variability is attenuated in postmenopausal women and unaffected by estrogen therapy

Delayed heart rate (HR) recovery in the immediate postexercise period has been linked to adverse cardiovascular prognosis. The after effects of an acute bout of exercise on HR modulation in postmenopausal women (PMW) and the influence of estrogen therapy are unknown.In 13 sedentary PMW (54 ± 2 y, mean ± SEM), we assessed HR variability (HRV) -an index of HR modulation-and the influence of estrogen therapy on HRV. HRV in the frequency domain was quantified during supine rest and again 60 minutes after treadmill exercise for 45 minutes, at 60% VO2peak. PMW were studied before and after 4 weeks of oral estradiol. To obtain reference values for the after effects of exercise on HRV in healthy young women, 14 premenopausal women (PreM) completed the identical exercise protocol.Compared with PreM, PMW demonstrated lower high frequency (vagal modulation) and total HRV (P < 0.05) at rest. In PreM, all HRV values were similar before and after exercise. In contrast, in PMW after exercise, despite having identical HR to PreM, high frequency and total HRV were all lower (all P ≤ 0.01) compared with pre-exercise HRV values. Estrogen therapy had no effect on pre or postexercise values for HRV.When compared with PreM, PMW have identical HR, but lower vagal HR modulation at rest and delayed HRV recovery after exercise. Estrogen does not restore baseline HRV or accelerate HRV recovery postexercise, suggesting aging rather than estrogen deficiency per se may lower HRV in PMW

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 cycling. After pre-determining peak oxygen uptake (VO2peak), we compared contra-lateral fibular nerve MSNA during 2 minutes each of mild (unloaded) and moderate (30-40% of the work rate at peak VO2, halved for single leg) 1-leg cycling in 18 young (23±1 years [mean±SE]) and 18 middle-aged (57±2 years) sex-matched healthy subjects. Mean height, weight, resting heart rate (HR), systolic blood pressure (BP) and percent predicted VO2peak were similar between groups. Middle-aged subjects had higher resting MSNA burst frequency and incidence (P<0.001) and diastolic BP (P=0.04). During moderate 1-leg cycling, older subjects’ systolic BP increased more (+21±5 vs.+10±1 mmHg; P=0.02) and their fall in MSNA burst incidence was amplified (-19±2 vs. -11±2 bursts/100heartbeats; P=0.01) but because HR rose less (+153 vs.+192 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 BP and a larger fall in MSNA