Non-Linear Analyses of Heart Rate Variability During Heavy Exercise and Recovery in Cyclists

Abstract

We investigated the time course of RR interval variability during exercise and subsequent 50 minutes of recovery in seven well-trained male cyclists who performed an exercise with 3 successive 8 min stages at 40 %, 70 % and 90 % of their maximal oxygen uptake. The goal of the study was to check whether the decrease in the amplitude of heart rate variability during heavy exercise was accompanied by changes in the chaotic structure of the fluctuations. Heart rate variability was analysed in the temporal and frequency domain using traditional tools and using non-linear methods (Largest Lyapunov Exponent, Detrended Fluctuation Analysis, Minimum Embedding Dimension). When compared to rest, variability at the heaviest exercise intensity was significantly lower (RR: 0.94 +/- 0.22 vs. 0.34 +/- 0.01 ms; SDRR: 0.11 +/- 0.04 vs. 0.01 +/- 0.00 ms) due to a decrease in both LF (2101 +/- 1450 vs. 0.14 +/- 0.09 ms (2) . Hz (-1)) and HF spectral energy (1148 +/- 1126 vs. 7.88 +/- 9.24 ms (2) . Hz (-1)). Non-linear analyses showed that heart rate variability remained chaotic whatever the exercise intensity (the largest Lyapunov exponent was positive at 90 % of the maximal oxygen uptake), with a fractal organisation that tended towards white noise (DFA value close to 0.5) during heavy exercise. During recovery, temporal and spectral variables came back to their rest values within about 30 minutes following an exponential pattern. Non-linear analyses revealed that heartbeat dynamics were disorganised at the beginning of recovery, and involved more regulating systems than at rest, even after 50 minutes of recovery. We concluded that, during heavy exercise, heart rate variability was mainly influenced by other factors than autonomous nervous system, and suggest that mechanical or neurological couplings between the cardiac, locomotor and respiratory systems could play an important part in the observed changes.

Heart rate variability is related to training load variables in interval running exercises

“…Also during heavy exercise, heart rate variability may be influenced by other factors than the ANS. Mechanical or neurological coupling between the cardiac, locomotor and respiratory systems could play an important part in the observed changes (Bernardi et al 1990;Casadei et al 1996;Casties et al 2006;Pichon et al 2004). …”

“…The frequency domain methods are perhaps the most widely used in exercise/training studies investigating HRV, but they have methodological limitations that inhibit their use during changing autonomic conditions, like immediate recovery after exercise (Task Force, 1996). In the few studies that have investigated HRV recovery during the first minutes of recovery, HRV has been found to be significantly lower than resting values, and either starting to increase already during the first recovery minutes (Casties et al 2006;Goldberger et al 2006;Martinmäki & Rusko, 2008) or remaining blunted for several minutes before recovery begins (Buchheit et al 2007a;Oliveira et al 2013). Differences in the results may be, at least partly, explained with differences in the physical TL of the preceding exercises as well as in the training status of the subjects.…”

“…Differences in the results may be, at least partly, explained with differences in the physical TL of the preceding exercises as well as in the training status of the subjects. Casties et al (2006) studied HRV of male cyclists before, during and 50 minutes after a graded 30 min exercise session at 40-90% VO2max. According to their results, the increase of HRV, RMSSD30s to be more specific, began already during the first 10 min of the recovery and further increase was observed during the succeeding 50 min of recovery.…”

“…The main hypothesis was that especially after highintensity exercises during which the energetic demands are increased, including significantly increased sympathetic activity, vagal activation is diminished (Casties et al 2006;Goldberger et al 2006). This could be detected on decreased post-exercise HRV.…”

“…In addition, increased exercise intensity has been found to have an effect on HRV after exercise, both during early (Casties et al 2006;Goldberger et al 2006;Martinmäki & Rusko, 2008) and later recovery (Buchheit et al 2007a;Gladwell et al 2010;Parekh & Lee, 2005;Saboul et al 2015;Seiler et al 2007;Terziotti et al 2001).…”