A paradigm shift in locomotion mechanics: collision loss explains functional requirements

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Terrestrial locomotion is energetically expensive and is a critical feature of the energy balance of active organisms such as mammals. Economical locomotion is commonly attributed to 'recovery' of energy within the stride cycle. However, this perspective leaves unanswered a number of questions about the source of the cost of locomotion and what this means to the functional design of animal. In order to properly interpret the functional consequences of adaptive modifications of the locomotory system in terrestrial forms it is necessary to understand the source of the mechanical cost of locomotion. This program of study is constructed around the novel perspective that terrestrial locomotion requires dissipative collisions with the ground and it is this loss that accounts for the major energy expenditure in locomotion. Collision losses have only recently been identified as a factor in human locomotion, and have been generally neglected in animal locomotion. My lab has successfully demonstrated the role of collision loss in locomotion systems as varied as ape brachiation and horse galloping. Applicability to such diverse types of locomotion strongly suggests that this perspective defines a new paradigm in animal locomotion. Demonstration and verification of the collision cost perspective in locomotion will require a coordinated synthesis between modeling and experimental evaluation. The research program has the potential to provide a substantial influence on the perspective of locomotion research and the evaluation of movement strategies in mammals in general. Though more complex, the analysis of overground locomotion has more general implications for organismal biology, whether in mammalian clades or expanded to other important groups. Examples of applicable problems include the interpretation of locomotion in extinct mammals, archosaurs (dinosaurs) or the transition from quadrupedal to bipedal locomotion in human ancestors.