Failure of accentuated vertical body movements to induce cardiac-locomotor coupling.

Cardiac-locomotor coupling (CLC) has been reported during a variety of rhythmic human activities. One reason postulated for such coupling is that axial movements of the viscera during some activities (the "visceral piston") may enhance expulsion of blood from the heart; if so, accentuated vertical movements of the body should provide a powerful stimulus to coupling. To test this hypothesis, we studied 20 subjects hopping and 20 others skipping rope for greater than or equal to 10 min while electrocardiographic and force-platform signals were recorded, from which we derived the subjects' exercise and heart rates. The incidence and intensity of apparent coupling in the test subjects were compared with those of cross-over controls, where the heart rate of each subject was related to the hopping or skipping rate of a matched subject. Ratios consistent with coupling were seen in 10 (50%) hopping subjects under test conditions and in 13 (65%) under control conditions; among skipping subjects, the incidences were 11 (55%) and 10 (50%). In neither group of subjects was the difference in the incidences or the intensities of apparent CLC statistically significant. Our failure to detect CLC while our subjects were hopping or skipping suggests that the visceral piston is unimportant to the CLC phenomenon.