Adaptive properties in the dynamics of the human locomotor -respiratory system

The purpose of this dissertation was to gain insight into the integration of the locomotory and respiratory systems by studying the coordinative behaviors that emerge in response to changing constraints. This was accomplished by utilizing analytical methods that have recently provided new insights into their adaptive strategies. Three studies were carried out that focused on different specific constraints that influence the interaction of the locomotory and respiratory systems. The first study investigated the relationship between stride frequency and locomotor-respiratory coordination (LRC) and the effect of LRC on the metabolic cost and ventilatory efficiency during running. It was found that stride frequency is a critical parameter affecting LRC and that the strength of LRC was not related to lower metabolic cost during running. In contrast, greater strength of coordination observed during running at preferred speed was associated with lower ventilatory efficiency. The second study examined the influence of mechanical constraints on LRC. The magnitude of mechanical perturbations imposed on the respiratory system by the upper body were not related to the strength of LRC. Instead, the timing within the stride cycle influenced the nature of LRC variability. It is likely that the coupling between these rhythms is not a passive mechanism but is related to active muscular control of the upper body, primarily influencing the variability of the coupling. The third study investigated the relationship between LRC and upper body control under normal and challenged postural and ventilatory conditions. These challenges resulted in significant changes in upper body control strategies including increases in the variability of motion. The postural challenge, however, did not act to further couple the respiratory rhythm to the locomotor rhythm and the ventilatory challenge did not act to decouple the rhythms. Together, the results of the current set of experiments illustrate the importance of variability in LRC and that mechanical constraints do not act to couple respiration to movement during human locomotion, as is typically assumed. Finally, the integration of upper body control and respiration has important implications for the study of gait stability