Coupling of cardiac and locomotor rhythms

Abstract

The pressure within exercising skeletal muscle rises and falls rhythmically during normal human locomotion, the peak pressure reaching levels that intermittently impede blood flow to the exercising muscle. Speculating that a reciprocal relationship between the timing of peak intramuscular and pulsatile arterial pressures should optimize blood flow through muscle and minimize cardiac load, we tested the hypothesis that heart rate becomes entrained with walking and running cadence at some locomotion speeds, by means of electrocardiography and an accelerometer to provide signals reflecting heart rate and cadence, respectively. In 18 of 25 subjects, 1:1 coupling of heart and step rates was present at one or more speeds on a motorized treadmill, generally at moderate to high exercise intensities. To determine how exercise specific this phenomenon is, and to refute the competing hypothesis that coupling is due to vertical accelerations of the heart during locomotion, we had 12 other subjects cycle on an electronically braked bicycle ergometer. Coupling was found between heart rate and pedaling frequency in 10 of them. Cardiac-locomotor coupling appears to be a normal physiological phenomenon, and its identification provides a fresh perspective from which to study endurance.

Coupling of breathing and movement during manual wheelchair propulsion.

“…Although LRC was investigated in the present study, it is likely that coupling may exist between the motor subsystem and other physiological subsystems that support it, like the cardiovascular system. Cardiac-locomotor coupling has been demonstrated in lower-limb activities (e.g., Kirby, Nugent, Marlow, MacLeod, & Marble, 1989) but has not yet been tested in any upper-limb activities. Investigation of coupling across different physiological subsystems will strengthen the understanding of both the coupling source and coupling behavior during transitions, which may or may not be the same for different pairs of subsystems.…”

Cardiolocomotor phase synchronization during rhythmic exercise

“…Kirby and collaborators note CLS during walking and running on a treadmill, as well as during a cycle ergometer exercise in humans 7) . In their experiment, CLS was considered to be present if the difference between the heart and step rates were less than 1.0%.…”

“…It should be noted, however, that their analysis was based on data from single subject designs. Kirby and collaborators 7,8,14) previously proposed in their series of experiments that CLS might improve blood supply to the contracting muscles to minimize skeletal muscle ischemia and/or minimize the energy cost of cardiac muscle contraction. They noted that muscle blood flow through active muscles is periodically occluded during each contraction phase of rhythmic exercise, possibly because IMP often rises beyond the level of systolic blood pressure during contraction 52,53) .…”

“…Phase synchronization between heartbeats and locomotor activity also occurs. Starting from the pioneering work of Coleman 5,6) in 1921, cardio-locomotor synchronization (CLS) has been documented in humans performing various locomotor activities, such as walking, running and cycling [7][8][9][10][11][12][13] . Surrogate data analysis has indicated that the emergence of CLS is more than just a coincidence of the rhythmic processes of cardiac and locomotor cycles, but is likely a consequence of heartbeat entrainment by locomotor rhythms due to interaction 12,13) .…”

Possible mechanism for modulating cardiovascular system during running in humans

“…A large cardiac output is the major factor distinguishing champion endurance athletes from other well-trained athletes. Researches from [3][4] [5] suggest that synchronization between the heart rate and the step rate during running may favor an athlete with moderate increase in cardiac output. To further explore it, we did a simulation study in order to get some insight into this phenomenon.…”