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Cumulative effects of successive bouts of maximal exercise on heart rate fluctuations

The aim of the present study was to investigate the cumulative effects of two bouts of maximal exercise on heart rate (HR) by spectral and detrended fluctuation analysis (DFA). Rowers (n=14, 11 males, 24±6 years old) performed two maximal (2k1 and 2k2) tests. HRV and DFA were calculated before (PRE1) and after 2k1 (POS1), four hours after POS1 (PRE2) and after 2k2 (POS2). The HF power was reduced from PRE1 (1527±1349 ms2) to POS1 (224±339 ms2) and from PRE2 (908±861 ms2) to POS2 (214±234 ms2, respectively, p<0.05) and in PRE2 was lower than PRE1 (p<0.05), with similar reductions in POS1 and POS2 (p>0.05). DFA in the time domain was used as a non‐linear method to quantify HR fluctuations detrended from its nonstationary background, giving a more precise measure of the fractality and long‐range correlations in the time series. DFA analysis is able to assess that HR fluctuations in POS2 were lower that POS1, moreover, the exponent α related to the fractal measure departs from a purely random one (α=0.5), evidencing long‐range correlations in HR variability, with slightly different exponents in PRE and POS groups. DFA showed that after 2k2 there was an additional reduction on HR fluctuations. These data suggest cumulative effects of exercise on HR dynamics and both methods give complementary information.