Non-linear dynamics of heart rate variability in athletes: effect of training

Only few studies on heart rate variability (HRV) in athletes have been performed so far. Moreover most of the data were obtained from time or frequency analysis. The aim of the present work was to use methods of nonlinear dynamics to study heart rate variability in a young population consisting of athletes and a sedentary group, used as controls. ECG episodes lasting 10 min were recorded digitally in supine position in a group of 34 young subjects. Spectral analysis was performed with Fast Fourier transform (FFT). Following non-linear methods were computed: fractal dimension, 1/f slope, approximate entropy (ApEn) and Lyapunov exponent. Major difference between controls and aerobic athletes was in resting heart rate. ApEn correlated well with power spectral density. Aerobic athletes showed a difference with controls in ApEn and Lyapunov exponent. Results indicate a possible relation of non-linear indices and autonomic regulation of cardiovascular function.