| Abstract: | Low heart rate variability (HRV) has been reported to be an independent risk factor for the development of coronary heart disease in women and has recently been identified as a risk factor for cardiac sudden death and all-cause mortality. We have recently demonstrated that endurance-trained post-menopausal women demonstrate higher levels of HRV than sedentary control subjects. The purpose of the present study was to test the hypothesis that 12 weeks of regular aerobic exercise would increase HRV in sedentary post-menopausal women with elevated arterial blood pressure (BP) (i.e. either high normal BP or stage I hypertension). A secondary aim was to test the hypothesis that the increase in HRV with exercise training, if observed, would be associated with an increase in spontaneous cardiac baroreflex sensitivity (SBRS), an important physiological determinant of HRV. To accomplish these aims, we studied eight sedentary post-menopausal women (age=54·5±1·3 years) before and after 12 weeks of aerobic exercise training (3·3±0·3 days per week at 70%±2% of maximal heart rate for 43±3 min per day). Maximal oxygen uptake and body weight did not change (P>0·05) with training, but percentage fat (35·5±2·6% vs. 34·5±2·3%, P<0·05) decreased and treadmill time to exhaustion increased (9·8±0·5 vs. 11·3±0·5 min, P<0·05). Supine resting levels of heart rate, RR interval and the standard deviation of the RR interval (time domain measure of HRV) were unchanged (all P>0·05) from baseline levels after 12 weeks of aerobic training. Similarly, the high-frequency, low-frequency and total power of HRV (frequency domain measures) were also unchanged from baseline (all P>0·05). SBRS was also not different before and after aerobic exercise training (1062 vs. 1363 ms mmHg?1 respectively, P>0·05). In contrast, systolic and diastolic BP were reduced approximately 8 and approximately 5 mmHg with training (both P<0·05) respectively. These results indicate that 12 weeks of moderate-intensity aerobic exercise training does not increase HRV or SBRS, despite producing a clinically significant reduction in BP at rest in post-menopausal women with elevated BP. Considered together with our previous findings in female master endurance athletes, these findings suggest that more intense and prolonged exercise training may be required to produce increases in HRV and SBRS in sedentary post-menopausal women. |
