The analysis of oscillations in heart rate (HR) and blood pressure (BP) has been used to assess indirectly the control of the circulation by the autonomic nervous system. Little is known of the effect of physical fitness on these measures. Fitness is associated with reductions in rest and exercise heart rate, probably to be due to increased vagal drive and reduced sympathetic tone. Training has been assessed in two conditions associated with abnormal autonomic control.

In hypertensive subjects BP is lowered by strenuous physical training. This is associated with an increase in HR variability and an increased baroreflex sensitivity assessed either by the bolus phenylephrine method or by two-way autoregressive bivariate cross-spectral analysis of HR and BP fluctuations.

In chronic heart failure a controlled trial of physical training has shown a significant reduction in low frequency HR oscillations and increases in high frequency oscillations, associated with a reduction in resting noradrenaline spillover assessed by radiolabelled tracer techniques. The changes in HR variability correlated well with both compliance with training and with improvement in exercise capacity.

Training can alter the patterns of HR and BP variations in a variety of conditions and the changes suggest a shift away from sympathetic predominance.