Transfer function gain between heart period and QT interval variability decreases at a 10-year follow-up in half-marathon runners

In the last years there is increasing interest in the study of the effects of physical activity on the cardiovascular control of athletes by heart period (HP) and QT interval (QT) variability analysis. However, the relation between HP and QT variability in athletes has been poorly investigated. Therefore, we aimed at estimate transfer function gain (TFG) to typify the relationship between HP and QT variability in athletes. We acquired electrocardiogram in 18 half-marathon runners while supine (REST) and during active standing (STAND) at baseline (B) and at a 10-year follow up (FU). The TFG was computed as the ratio between the modulus of the cross-spectral density between HP and QT divided by the power spectral density of HP in low frequency (LF, 0.04-0.15 Hz, TFGLF) and high frequency (HF, 0.15-0.4 Hz, TFGHF) bands. We found that TFGHF was lower at FU compared to B both at REST and during STAND. TFGLF increased during STAND compared to REST only at FU. The present work supports the use of the linear approach in the frequency domain to typify the cardiac control of athletes. In addition, the findings suggest that a moderate and regular physical activity through the years is beneficial as it favors a decrease of the cardiac sympathetic modulation.