Abstract
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 (τoff) have been widely studied, but less attention was devoted to the time delay (tdelay) 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 tdelay and τoff. 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 tdelay and τoff. Both (LF/HF)REST and (LF/HF)RECOV had a skewed distribution. Significant rank correlation was found for (LF/HF)REST vs. τoff and for (LF/HF)RECOV vs. both τoff and tdelay. The difference (LF/HF)RECOV–REST had a normal distribution and a strong partial correlation with tdelay but not with τoff. Thus, a long tdelay marks a sympathetic activity that keeps high after exercise, while a high sympathetic activity before sprint leads to a slow recovery (high τoff), seemingly accompanying a poor performance.
Highlights
Current studies have widely reported the role of heart rate (HR) kinetics after exercise in predicting health issues such as cardiac disease, heart failure, and sudden death (Imai et al, 1994; Aeschbacher et al, 2016; Qiu et al, 2017)
It is apparent that HR started to rise in advance of the 60-m sprint, as the subject was readying itself to the effort
The last 2 min of standing rest and the first 2 min after sprint end were excluded from HR variability (HRV) analysis
Summary
Current studies have widely reported the role of heart rate (HR) kinetics after exercise in predicting health issues such as cardiac disease, heart failure, and sudden death (Imai et al, 1994; Aeschbacher et al, 2016; Qiu et al, 2017) It is well known (Task Force of the European Society of Cardiology the North American Society of Pacing Electrophysiology, 1996) that the analysis of HR variability (HRV) needs a steady-state HR kinetic, or at least a linear trend of the signal, in order to reliably calculate variability indices like the SD of R-R intervals and the root mean square of successive differences (in the time domain), or the spectral components of HRV (in the frequency domain). It is worth noting that a low LF/HF ratio, reflecting a generally high vagal tone, has been shown to be associated with a better cardiac adaptation to daily life exercise or activities (Peçanha et al, 2014)
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