  The aim of this paper is to investigate the cardiorespiratory synchronization
in athletes subjected to extreme physical stress combined with a cognitive
stress tasks. ECG and respiration were measured in 14 athletes before and after
the Ironmen competition. Stroop test was applied between the measurements
before and after the Ironmen competition to induce cognitive stress.
Synchrogram and empirical mode decomposition analysis were used for the first
time to investigate the effects of physical stress, induced by the Ironmen
competition, on the phase synchronization of the cardiac and respiratory
systems of Ironmen athletes before and after the competition. A cognitive
stress task (Stroop test) was performed both pre- and post-Ironman event in
order to prevent the athletes from cognitively controlling their breathing
rates. Our analysis showed that cardiorespiratory synchronization increased
post-Ironman race compared to pre-Ironman. The results suggest that the amount
of stress the athletes are recovering from post-competition is greater than the
effects of the Stroop test. This indicates that the recovery phase after the
competition is more important for restoring and maintaining homeostasis, which
could be another reason for stronger synchronization.
