Doctoral Dissertation Improvement Grant: The Effect of Hindlimb Length on Running and Walking Performance

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Despite decades of research on locomotor energetics, the role of leg length in determining locomotor energy efficiency and speed remains unclear. This project will investigate the effect of leg length on energy cost and speed during walking and running in human and domestic dogs in order to test a new biomechanical model that incorporates leg length as a determinant of these performance variables. Energy expenditure will be measured at a range of walking and running speeds for both species during treadmill trials. A set of outdoor trials will also be conducted in order to test the effect of leg length on maximum running speed and acceleration, and to investigate tradeoffs between energetic efficiency and maximum speed and acceleration. Results will be used to test predictions of the model, specifically that increased leg length improves energy efficiency and speed during walking and running, but at the cost of decreased acceleration and increased energy necessary to swing the leg. The inclusion of both bipeds (humans) and quadrupeds (dogs) will further provide a means of investigating the link between leg length and locomotor performance across a range of anatomical design. If successful, the model will provide a new method of quantitatively assessing locomotor performance in both living and fossil species by providing a new, potentially more accurate and reliable means of making inferences about locomotor behavior and evolution. As the evolution of the genus Homo is marked by a significant increase in leg length, this model will be especially useful in testing current hypotheses regarding the evolution of hominid locomotor and foraging behavior.Given the diversity of locomotor adaptations evident in living and extinct species, the inability to predict locomotor performance reliably and quantitatively from limb design represents a significant shortcoming in our understanding of locomotor adaptation and ecology. This study will address this issue by testing a relatively simple model that explicitly incorporates leg length as a determinant of locomotor energy cost, and by testing the effect of leg length on maximum and preferred speeds. This project also will promote the integration of graduate training and research in physical anthropology with experimental physiology and biomechanics.