Date of Award

5-13-2011

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Kinesiology

First Advisor

Graham E. Caldwell

Second Advisor

Brian R. Umberger

Third Advisor

Joseph Hamill

Subject Categories

Kinesiology | Motor Control

Abstract

Humans generally use two modes of locomotion as adults. At slow speeds we walk, and at fast speeds we run. To perform either gait, we use our muscles. The central questions in this dissertation were: (1) Why do humans run the way they do, and (2) How do the mechanical properties of muscle influence running performance? Optimal control simulations of running were generated using a bipedal forward dynamics model of the human musculoskeletal system. Simulations of running and sprinting were posed as two-point boundary value problems where the muscle excitation signals were optimized to maximize an optimality criterion. In the first study, minimizing the dimensionless muscle activations rather than the cost of transport generated the simulation that most closely agreed without experimental kinetic, kinematic, and electromyographic data from human runners. In the second study, sprinting simulations were generated by maximizing the model’s horizontal speed. Adjustments in the parameters of the muscle force-velocity relationship, in particular the shape parameter, increased the maximum speed, and provided support for previous theories on limitations to maximum human sprinting speed. In the third study, virtual aging of the model’s muscles induced changes in the running biomechanics characteristic of older adults, and increased the stresses and strains of muscles where older runners are more frequently injured than young runners. Strengthening these muscles reduced their loading while still maintaining an economical gait with a relatively low joint contact force at the knee. The studies provide a framework for testing hypotheses on human movement without a strong dependency on experimental data, and provided new evidence on the validity of the simulation approach for studying human running, and on optimality criteria in human running, limitations to maximum sprinting speed, and relationships between aging, muscular properties, and running injuries.

Included in

Motor Control Commons

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