Elevated heart rate variability in physically active young and older adult women.

1. Low heart rate variability is associated with an increased risk of cardiac sudden death, coronary heart disease and all-cause mortality. We have previously shown that physically active postmenopausal women demonstrate higher levels of heart rate variability and cardiac baroreflex sensitivity compared to their sedentary peers. The purpose of the present prospective study was to test the hypothesis that heart rate variability and cardiac baroreflex sensitivity would be reduced with age in sedentary but not physically active women. To accomplish this, we measured heart rate variability (both time and frequency domain) and spontaneous cardiac baroreflex sensitivity (SBRS, sequence method) in the sitting posture in 23 sedentary women [11 premenopausal and 12 postmenopausal (age, 28 +/- 1 and 61 +/- 2 years; VO2max, 35.3 +/- 1.4 and 21.7 +/- 1.5 ml.min-1.kg-1 respectively] and in 22 physically active women [12 premenopausal and 10 postmenopausal (age, 31 +/- 1 and 59 +/- 2 years; VO2max, 52.5 +/- 1.4 and 39.7 +/- 1.8 ml.min-1.kg-1)]. 2. The S.D. of the R-R interval (time domain) was reduced (P < 0.05) with age in both sedentary (52 +/- 6 versus 33 +/- 4 ms) and physically active women (72 +/- 8 versus 49 +/- 9 ms). The high-frequency power (3740 +/- 1527 versus 915 +/- 188 and 9516 +/- 2849 versus 2803 +/- 1083 ms2/Hz), total power of heart rate variability and SBRS (11 +/- 2 versus 7 +/- 2 and 19 +/- 3 versus 13 +/- 2 ms/mmHg) also demonstrated similar age-related reductions in sedentary and physically active women, respectively (all P < 0.05). The S.D. of the R-R interval, high-frequency and total power of heart rate variability, and SBRS were higher (all P < 0.05) in the physically active compared with the sedentary women at any age. There was no significant influence of age or physical activity status on the low-frequency power of heart rate variability. In addition, no significant differences in any of the time or frequency domain measures of heart rate variability or SBRS were observed in users compared with non-users of hormone replacement therapy. 3. The results of the present study suggest that heart rate variability and cardiac baroreflex sensitivity decline similarly with age in healthy sedentary and physically active women. However, physically active women demonstrate higher levels of heart rate variability and cardiac baroreflex sensitivity compared with their sedentary peers, regardless of age.