Heart Rate Kinetics and Sympathovagal Balance Accompanying a Maximal Sprint Test

During a sprint test, Heart Rate (HR) quickly increases, keeps high for some seconds and returns to basal value with a roughly exponential decay. While the decay and its time constant (tau-off) have been widely studied, much less attention has been devoted to the time delay (Tdelay) between the sprint end and the HR decay onset. Given the proven correlation between the sympathovagal balance and the exercise performance, as well as the frequent heart failures in cardiopath patients during the post-exercise phase, we evaluated the sympathovagal balance before and after the sprint, trying to correlate it with both Tdelay and tau-off. R-R intervals, recorded in 24 healthy adults for 5 min before, during and for 5 min after a 60-m sprint test (from Storniolo JL, Pavei G, Minetti AE. 2017 Front Physiol 8:868, with kind permission of all Authors), were re-processed by autoregressive method, so as to extract the HR variability power (LF and HF) in the low and high frequency ranges, respectively. The sympathovagal balance, estimated as the ratio LF/HF before (bef) and after (aft) exercise, was correlated with Tdelay and tau-off. Both (LF/HF)bef and (LF/HF)aft had a skewed distribution. Rank correlation (p<0.05) was found for (LF/HF)bef vs. off (r=0.42) and for (LF/HF)aft vs. both off (r=0.41) and Tdelay (r=0.43). The difference (LF/HF)bef-aft had a normal distribution and a strong partial correlation with Tdelay (r=0.61) but not with tau-off. Thus, a long Tdelay well fits with a high sympathetic activity after exercise, while an already high sympathetic activity before sprint leads to a slow recovery (high tau-off), which should accompany a poor performance. These results confirm that the autonomic modulation plays an important role in both parameters depicting HR kinetics after a sprint test.