| Description |
Integration of locomotion and respiration has been critical in the evolution of many mammals that are specialized for sustained locomotion. Humans are unique among mammals in using a striding bipedal gait. Despite increased flexibility in breathing patterns associated with bipedalism, humans, like quadrupedal mammals, exhibit locomotor-respiratory coupling (LRC) during high speed running. Galloping mammals typically use a 1: 1 (strides/breath) LRC ratio; humans, however, use a wider set of coupling ratios, with 2: 1 being the most common. It is not known whether or not locomotor-respiratory coupling has any functional significance in humans. To explore this issue, the mechanical interactions between locomotion and breathing were examined in humans running on a treadmill. We ran four adult subjects on a treadmill over a series of speeds that were within their comfort range. Pneumotachographs measured inspiratory and expiratory flow separately, while an accelerometer attached to the top of the head measured vertical trunk acceleration, which reflected the step cycle. The correlation between body motion and the accelerometer signal was periodically checked by synchronized video recordings. These data were analyzed by determining the coupling patterns, together with the phase angles of various respiratory events relative to the step cycle. All four subjects showed a strong bias toward the initiation of inspiration and expiration around heelstrike, despite the fact that only two were coupled runners. This suggests that there are functionally meaningful mechanical interactions between locomotor forces and respiratory flow in human runners. Furthermore, the oscillations (accelerations) in the respiratory flow traces were found to have consistent phase relationships to the locomotor cycle. This strongly implies that locomotor forces induce such perturbations in ventilatory flow. In addition, those inspirations and expirations that begin outside the regions of the step cycle normally "preferred" for initiation have significantly lower initial acceleration of flow. Based on these results, I propose a preliminary mechanical model to describe the interactions between locomotor forces and ventilation. This model makes specific predictions that may lay the groundwork for possible future research on locomotorrespiratory interactions in humans. |
