Purpose: This study aimed at testing the hypothesis that positive cardiolocomotor coordination (CLC) measure occurs by chance during a running task where the heart rate (HR) is approximated to the step frequency (StepF).
Methods: The electrocardiogram and electromyogram from the right gastrocnemius lateralis muscle were continuously recorded from ten healthy young men running at a paced rhythm of 152 step/min, to monitor HR and StepF. CLC was evaluated by phase synchrograms and the index of conditional probability (iCP). Results were validated with surrogate data and a crossover approach, where the HR of one subject was related to the StepF of another one, and comparisons were made combining subjects two by two.
Results: Six subjects showed synchrogram structures and high iCP values (≥0.8), suggesting the occurrence of physiological entrainment, when the HR reached the SF range. In crossover analysis, phase synchrograms and iCP presented similar behavior of original data when the HR from one subject was close enough to the SF from another one. Significant iCP values in 46 of 90 comparisons (51%) were observed, including all cases crossing signals among the six positive cases.
Conclusion: Synchrogram and iCP tools currently employed for measuring CLC are not appropriate because they indicate the occurrence of this phenomenon even among subjects who ran on different days and times of each other.
Keywords: Cardiolocomotor coupling; Crossover evaluation; Induced rhythm; Physiological entrainment.