Doctor of Philosophy (PhD)
First Committee Member
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Biomechanics studies over the past 150 years, suggest that animals, including humans, move at speeds that “optimize” their cost of transport. These optimizations can be metabolic, mechanical, or a mixture of the two; however, the consensus on the relationship between metabolic and mechanical cost has been muddied by our current conceptualizations of mechanical cost. Our prior considerations in assessing mechanical cost of transport for animal locomotion often rely upon the exchange of potential and kinetic energy for a rising and falling center of mass that is supported by rigid legs. As a result, our understanding of the mechanical costs associated with two-legged walking, especially the like that of humans, remains incomplete. Established approaches model only the mechanical cost of the step-to- step transitions, and often neglect or minimalize the cost dynamics that occur during steps. In an effort to rectify our current assumptions about mechanical cost, I examine the walking gaits of people through the lens of a quantitative approach that considers every instance of the walking stride as a whole. Direct measurement of ground reaction force and center of mass velocity vector geometries provides an opportunity to quantify the fundamental mechanical cost of transport dynamics that are inherent to human walking. The novel aspect of my approach allows for the partitioning of the human walking stride into steps (single support periods) and step-to-step transitions (double support periods). My approach allows us to better ascertain each support periods’ respective contributions to the overall mechanical work that is inherent to moving our body weight over a unit of distance in two steps – i.e. the mechanical cost of transport.
My studies on human volunteers include experimental perturbations of walking speed and I also consider the effect of foot-ankle prosthetic devices on people with below-the-knee amputations. After establishing mechanical cost of transport dynamics on able-bodied volunteers walking at different speeds, I compare these results to the walking gaits of people using non-motorized, dynamic prosthetics and found that while mechanical costs of transport did not greatly differ between the two groups, the distribution of mechanical cost throughout the walking stride for prosthesis users was quite asymmetric. These cost asymmetries often resulted in “hot spots” of mechanical cost that have the potential to be rectified through mechanical intervention in the form of mechanical tuning or robotic prosthetic applications. I show this potential through the experimental examination of a prototype, powered prosthesis that was designed to emulate human ankle dynamics at different walking speeds. The results of the robotic intervention showed a 12%-17% decrease in overall mechanical cost of transport for prosthesis users versus their walking gait solutions on their traditional, non-motorized prosthesis. The results of this mechanical cost analysis along with stride partitioning to identify asymmetrical cost distribution is a key innovation for the analysis of human locomotion and has potential to bolster the foundation for future consideration of mechanical cost of transport dynamics in people using prosthetics, and in the development of robotic and movement assistance technologies.
Bipedal locomotion; Foot-ankle prosthetics; Human walking; Mechanical cost of transport; Robotic prosthetics
Biomechanics | Kinesiology
University of Nevada, Las Vegas
Isaacs, Michael Richard, "Partitioning the Mechanical Cost of Human Walking: Unveiling Cost Asymmetries for Bionic Technologies" (2020). UNLV Theses, Dissertations, Professional Papers, and Capstones. 3907.
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