Following a holistic approach, measures of brain cortical activity in relation to exercise-induced changes in autonomic control will allow a more detailed exploration of complex control mechanisms of fatiguing exercise. Therefore, the purpose of the current study was to investigate the influence of exercise duration and cycling cadence on total variability and complexity of heart rate variability (HRV) in relation to cortical activity measured with electroencephalography (EEG). Sixteen trained cyclists completed a 60min exercise session at 90% of the individual anaerobic threshold on a bicycle ergometer. Cadence was changed every 10 minutes (90-120-60-120-60-90 rpm), while the workload was held constant. RR-intervals and EEG were recorded continuously during exercise. Regarding HRV parameters, time domain measures (meanRR, SDNN) and fractal correlation properties were analyzed using the short-term scaling exponent alphal of detrended fluctuation analysis (DFA-alphal). Moreover heart rate (HR), blood lactate (La) and rating of perceived exertion (RPE) were recorded at regular intervals. In comparison to 60 and 90 rpm, participants` HR, La and RPE were increased during cycling at 120 rpm. Similarly, EEG spectral power in the total spectrum was increased at the highest cadence. In contrast, all analyzed HRV parameters showed decreased values from lower cadences to 120 rpm. Whereas HR increased over time when the beginning and the end of the constant workload with the same cadence at 90 rpm is compared, all analyzed HRV and EEG parameters decreased. The results show that exercise duration and cadence have an impact on metabolic, cardiac and nervous system parameters. In this respect, HRV values decreased over time and in response to higher cadences. This change may be due to increased or-ganismic stress and indicates a decrease in the overall variability as well as complexity of the RR-interval-fluctuations. The decrease of DFA-alpha 1 could also be associated with an organismic system withdrawal to ensure homeostatic protection. Recalling that this change was accompanied by a decrease of EEG spectral power, our findings provide new insights for the discussion of complex fatigue models and allow a more sophisticated analysis of organismic demands.
© Copyright 2018 Herzfrequenzvariabilität: Methoden und Anwendungen in der Sportwissenschaft, Arbeits- und Intensivmedizin sowie Kardiologie. 7. Internationales HRV-Symposium am 4. März 2017 in Halle (Saale). Veröffentlicht von Feldhaus, Ed. Czwalina. Alle Rechte vorbehalten.