Analysing entrainment of cardiac and locomotor rhythms in humans using thesurrogate data technique

Using the surrogate data technique we evaluated whether, during running, th e synchronization between cardiac and locomotor rhythms resulted from entra inment or by chance. An electrocardiogram and an electromyogram fi-om the r ight vastus lateralis muscle were monitored from ten healthy young men runn ing at a paced rhythm of 150 steps a minute. The relationship between cardi ac and locomotor rhythms was determined by examination of the occurrence of the heart beat with respect to the locomotor phase. The examination reveal ed that synchronization patterns were observed in all subjects. We generate d surrogate data by sorting randomly the original locomotor rhythm, and no synchronization patterns were then seen. This may indicate that the synchro nization between the cardiac and locomotor rhythms represented entrainment. We have provided the first evidence for the rejection of the hypothesis th at when heart beat rhythm is close to the locomotor rhythm, synchronization between the two rhythms occurs by chance.