NEURAL REGULATION OF HEART-RATE-VARIABILITY IN ENDURANCE ATHLETES AND SEDENTARY CONTROLS

Objective: The aim was to examine the cardiac autonomic responses to orthostatic stress and recovery from steady state exercise in endurance trained athletes and sedentary subjects. Methods: The power spectrum of heart rate variability was measured before and after exercise in 10 male long distance runners and 14 male sedentary control subjects. Both groups were comparable in sex, age, and body mass index. Continuous ECG recordings were obtained during the following physiological manoeuvres: 45 min supine rest state; 10 min standing; 15 min steady state exercise at 50% maximum workload, and 15 min while supine during post-exercise recovery. The resting heart rate of athletes was lower than controls, at 52(SD 4.9) v 67(8.7) beats-min-1, p<0.001. Power spectrum analysis was performed using autoregressive modelling. Results: The resting high frequency (HF) vagal component was higher in athletes than controls, at 62(10.7) v 44(22.4) beats.min-1.Hz-1, p<0.05. The resting low frequency (LF) peak power was significantly reduced in athletes, at 54(9.9) v 70(19.5) in control, p<0.05. Although no group differences were observed during upright posture or exercise, the LF:HF area ratio had already returned to pre-exercise levels within 5 min of recovery in athletes. Conversely, it required up to 15 min of recovery before a noticeable decrease in the LF:HF area ratio was seen in controls. Conclusions: These data support the hypothesis that endurance training modifies heart rate control in whole or in part through neurocardiac mechanisms.