Afferent somatosensory information as a possible cause of cardiac-locomotor coupling?

Cardiac-locomotor coupling (CLC), referring to the 1:1 synchronization of heart rate (HR) by locomotion, has not been satisfactorily explained as yet. Recent neuroanatomical research has shown that ergoreceptors have projections to the nucleus tractus solitarii, a brainstem structure where baroreceptor afferents also terminate. We have attempted to induce and demonstrate fictive CLC in 15 healthy young men in supine posture. Somatosensory ergoreceptor stimulation achieved by transcutaneous electrical nerve stimulation (TENS) at the feet at 1:2 HR/TENS ratio. The synchrogram tool was used to quantify synchronization, which was significant though weak in two separate sessions (3.1+/-0.1%, p<0.02 and 1.8+/-0.1%, p<0.04). These figures contain high level of occasional coincidence of frequencies (OCF) effect, emphasizing the caution required in any study aimed at quantifying synchronization. Future protocol will include 1:1 ratio in standing posture.