ANALYSIS OF COORDINATION BETWEEN BREATHING AND WALKING RHYTHMS IN HUMANS

We investigated the coordination between breathing and walking in huma ns to elucidate whether the coordination degree depends more on metabo lic load or on breathing or stride frequencies and whether coordinatio n causes energetic economization expressed by reduction of oxygen upta ke (Vo(2)). Eighteen healthy volunteers walked on a treadmill at three load levels realized by different velocities and slopes. We analyzed the time intervals between step onset and the onset of inspiration or expiration related to stride duration (relative phase, phi) and comput ed the relative-phase histogram to assess the degree of coordination. The degree of coordination between breathing and stepping enhanced wit h increasing walking speed. Increased work load achieved by slope at c onstant walking speed improved coordination only slightly. No signific ant Vo(2) reduction due to coordination was found. Vo(2) was more stro ngly related to ventilation variations occurring during coordination. Also the sympathetic tone reflected by the spectral power of heart rat e variability was not reduced during coordination. We conclude that du ring walking the coordination degree increases with increasing stride frequency and that coordination does not necessarily cause energetic e conomization.