Objectives. - We studied the influence of the "Square-Wave Endurance Exercise Test" (SWEET) training program on heart rate (HR) variability during supine rest, 60° upright position and submaximal constant exercise. Methods. - Beat-by-beat HR was recorded during 10 min in the three conditions in 14 healthy women. Before and after 6 weeks of training (45 min, three times a week; n = 7) or daily life (control group, n = 7), time- and frequency-domain analyses of HR variability were performed (standard deviation of interbeat interval, root mean square of successive differences, total-, low-, high-frequency power of HR variability). Results. - After training, HR decreased during supine rest, 60° upright and submaximal exercise, whereas time- and frequency-domain analyses of HR variability indices increased (P < 0.05). No significant changes were observed in the control group. Conclusion. - Six weeks of training by SWEET elicited an increase in heart rate variability (HRV) not only at rest, but also during orthostatism and submaximal exercise. It can, therefore, provide an useful training form in a large population of healthy or diseased people.
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