| Descript |
78 p |
| Note |
Source: Dissertation Abstracts International, Volume: 65-09, Section: B, page: 4700 |
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Chairs: Tony M. Keaveny; Claire T. Farley |
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Thesis (Ph.D.)--University of California, Berkeley, 2004 |
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People can easily run on a variety of terrains by adjusting the stiffness of their legs. The overall goal of this dissertation is to understand how humans adjust leg stiffness during hopping and running and to examine whether people strongly prefer specific frequencies for hopping and running due to the optimal role of the spring-like mechanics of the leg. To accomplish these goals, I investigated humans hopping on two legs vs hopping on one leg, running at a range of stride frequencies at a fixed speed, and hopping at a range of frequencies. When humans hop on one leg, they make their leg 59% stiffer than when they hop on two legs. Leg stiffness is most sensitive to changes in ankle stiffness and increased due to a stiffer ankle and a smaller moment arm of the ground reaction force about the ankle. In contrast, during running, leg stiffness is most sensitive to knee mechanics. Runners make their leg 96% stiffer to increase stride frequency primarily by stiffening the knee and decreasing the moment arm of the ground reaction force about the knee. The mechanisms to adjust leg stiffness differ due to the moment arm of the ground reaction force being longest about the ankle in hopping and about the knee in running. In the final study, I find that the leg does not behave most like a spring at the preferred frequencies for hopping and running. Rather, it becomes more spring-like as frequency increases. Thus, springlike leg behavior does not cause the minimization of metabolic energy cost at the preferred frequency. Overall, these studies emphasize the role of springlike leg mechanics and the importance of leg stiffness adjustment in hopping and running. Moreover, due to different leg geometries, hoppers and runners use different strategies for leg stiffness adjustment |
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School code: 0028 |
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DDC |
| Host Item |
Dissertation Abstracts International 65-09B
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| Subject |
Engineering, Biomedical
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Health Sciences, Recreation
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0541
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0575
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| Alt Author |
University of California, Berkeley
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