Rhythmic physical exercise as a protocol to study synchronization phenomenon

The phenomenon of synchronization, which appears during the coupling of two or more oscillators, is often observed in nature and many fields of science. The case of several rhythms is particularly interesting, as the synchronizations may compete. In this work, we report the occurrence of the phase coupling between three biological rhythms: heart rate, respiration and locomotor rhythm. We analyzed its appearance during cycling on a stationary bike with stepwise increasing speed. Presence of synchronization was investigated using the synchrogram in order to detect phase-locking epochs. Study group consisted of 21 young healthy volunteers (15 women and 6 men). Specific subgroups were also defined. During exercise synchronization between all rhythms appeared in all subjects. Cardiolocomotor synchronization occurred significantly more often, which underlines the role of cardiac entrainment to phasic baroreflex input. In cardiolocomotor synchronization we observed a direct phase coupling (1:1) lasting at least 20 s. It occurred in 76 % of subjects, which manifests a dominant role of this type of synchronization. Additionally, we observed subjects, in whom epochs of simultaneous synchronization of all rhythms appeared. Total duration of synchronization was significantly larger in men than in women and in less experienced cyclists. No significant difference in age or BMI was observed, however the group was relatively uniform. During the post-exercise epoch, cardiorespiratory synchronization appeared in nine subjects. Due to its frequent occurence, synchronization is a good candidate for an objective estimator of physical stress, applicable in diagnostic, therapeutical and lifestyle scenarios.