Heart Rate Kinetics and Sympatho-Vagal Balance Accompanying a Maximal Sprint Test

When a maximal sprint starts, heart rate (HR) quickly increases. After the exercise ends, HR keeps high for seconds before recovering with a roughly exponential decay. Such decay and its time constant (τ_off) have been widely studied, but less attention was devoted to the time delay (t_delay) between sprint end and HR decay onset. Considering the correlation between sympatho-vagal balance and performance, as well as the occurrence of heart failure in cardiopaths during the post-exercise phase, we evaluated sympatho-vagal balance before and after sprint, trying to correlate it with both t_delay and τ_off. R-R intervals, recorded in 24 healthy adults from 5 min before to 5 min after a 60-m sprint-test (from Storniolo et al., 2017, with permission of all authors), were re-processed to extract HR variability power (LF and HF) in the low- and high-frequency ranges, respectively. The sympatho-vagal balance, evaluated in pre-test resting period (LF/HF)_REST and at steady-state recovery (LF/HF)_RECOV, was correlated with t_delay and τ_off. Both (LF/HF)_REST and (LF/HF)_RECOV had a skewed distribution. Significant rank correlation was found for (LF/HF)_REST vs. τ_off and for (LF/HF)_RECOV vs. both τ_off and t_delay. The difference (LF/HF)_RECOV-REST had a normal distribution and a strong partial correlation with t_delay but not with τ_off. Thus, a long t_delay marks a sympathetic activity that keeps high after exercise, while a high sympathetic activity before sprint leads to a slow recovery (high τ_off), seemingly accompanying a poor performance.