Cardiolocomotor Interactions During Dynamic Handgrip and Knee Extension Exercises

Coupling of locomotor and cardiac rhythms has been described during various locomotor activities in humans1,5, 6,7,9,10. Although some prior work has attempted to clarify the advantage of the cardiac-locomotor coordination1,6,9, direct evidence showing the functional significance of such locomotor modulation of heart beats has not yet been presented. It has generally been suggested that the synchronization phenomenon is a manifestation of nonlinear biological oscillators in which an inherent phase dependency to the periodically imposed input is involved11. Therefore, we thought that a phase dependency of cardiac rhythm with respect to the muscle contraction may also exist, and this would help us to infer the mechanism of coupling and its physiological significance. The purpose of this study was to investigate how the cardiac rhythm interacts with the muscle contraction rhythm during exercise, and to examine whether the coupling has such functional significance that ensures the exercising muscle blood flow.