Effect of aerobic fitness training on heart rate variability and cardiac baroreflex sensitivity

The present study examined the effects of aerobic fitness training on heart rate variability and cardiac baroreflex sensitivity. It was specifically tested whether training influenced the reduction of heart rate variability and cardiac baroreflex sensitivity in response to emotional stress. Sixty-two sedentary subjects participated in four different treatments: 19 subjects were trained for 4 months after which they reverted to their sedentary habits (training/de-training); 19 subjects remained untrained for 4 months after which they tao completed a 4 month training programme (postponed training); 11 subjects exercised intensively for the entire 8 month period (long-term training), and 11 subjects remained untrained throughout. After 0, 4 and 8 months, heart rate, blood pressure, heart rate variability and the gain of the cardiac baroreflex were measured at rest, during two stressful laboratory tasks, and during a paced breathing condition. The FinApres system was used to obtain continuous tracings of the blood pressure waveform, and spectral analyses were used to compute the gain of the cardiac baroreflex. Before training, no cross-sectional association was found between VO2-max and heart rate variability or baroreflex sensitivity in any of the conditions. Furthermore, there were no effects of (de)training on resting levels of heart rate variability and the gain of the cardiac baroreflex, or on the stress-induced reduction in these parameters. The training manipulations only influenced fitness and the overall levels of heart rate and diastolic blood pressure. These results suggest that aerobic fitness training does not influence vagal tone or baroreflex sensitivity in either resting or emotionally taxing conditions.