BACKGROUND: Our group has shown a positive dose-response in maximal cardiorespiratory exercise capacity (VO2max) and heart rate variability (HRV) to 6 months of exercise training but no improvement in VO2max for women >= 60 years. Here, we examine the HRV response to exercise training in postmenopausal women younger and older than 60 years. METHODS: We examined 365 sedentary, overweight, hypertensive, postmenopausal women randomly assigned to sedentary control or exercise groups exercising at 50% (4 kcal/kg/week (KKW)), 100% (8 KKW) and 150% (12 KKW) of the National Institutes of Health (NIH) Consensus Development Panel physical activity guidelines. Primary outcomes included time and frequency domain indices of HRV. RESULTS: Overall, our analysis demonstrated a significant improvement in parasympathetic tone (rMSSD and high frequency power) for both age strata at 8 KKW and 12 KKW. For rMSSD, the age-stratified responses were: control, < 60 years, 0.20 ms, 95% confidence interval (CI) -2.40 to 2.81; >= 60 years, 0.07 ms, 95% CI -3.64 to 3.79; 4-KKW, < 60 years, 3.67 ms, 95% CI 1.55 to 5.79; >= 60 years, 1.20 ms, 95% CI -1.82 to 4.22; 8-KKW, < 60 years, 3.61 ms, 95% CI 0.88 to 6.34; >= 60 years, 5.75 ms, 95% CI 1.89 to 9.61; and 12-KKW, < 60 years, 5.07 ms, 95% CI 2.53 to 7.60; >= 60 years, 4.28 ms, 95% CI 0.42 to 8.14. CONCLUSIONS: VO2max and HRV are independent risk factors for cardiovascular disease (CVD) mortality. Despite no improvement in VO2max, parasympathetic indices of HRV increased in women >= 60 years. This is clinically important, as HRV has important CVD risk and neurovisceral implications beyond cardiorespiratory function.

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