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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Kinesiology

Year Degree Awarded

2016

Month Degree Awarded

February

First Advisor

Brian Umberger

Second Advisor

Graham Caldwell

Third Advisor

Jane Kent

Fourth Advisor

Frank Sup

Subject Categories

Biomechanics

Abstract

The human musculoskeletal system consists of several muscles crossing each joint. In the human lower limb, most major muscles cross either one or two joints; labeled as uniarticular or biarticular muscles, respectively. The major biarticular muscles of the leg are the rectus femoris, hamstrings, and gastrocnemius. Several suggestions have been proposed as to how biarticular muscles may reduce the metabolic cost of human movement. Using experimental protocols, it is difficult to address the energetic effects of biarticular muscles, as individual muscle contributions to human movement cannot be measured and there is no way to determine what the effect might be on the energetics of movement if instead of a biarticular muscle there were two equivalent uniarticular muscles. Therefore, this project used a musculoskeletal modeling approach to address the question of whether biarticular muscles reduce the metabolic cost of submaximal pedaling. We used one standard model representing a simplified human musculoskeletal design with 6 uniarticular and 3 biarticular muscles and created three different models, each replacing one biarticular muscle of the standard model with two mechanically equivalent muscles. The models with the altered musculoskeletal design could not be expected to pedal in the same manner as a human, so it was not possible to generate simulations of pedaling by tracking experimental pedaling data, a proven method for replicating submaximal pedaling computationally. Therefore, in the first study, we tested the ability of five performance-based criterion to generate predictive simulations of submaximal pedaling using the standard model. We found that minimizing muscle activations best replicated the general kinematics, kinetics and muscle excitation patterns of submaximal pedaling. In the second study, we used this performance-based criterion to generate pedaling simulations for the three new musculoskeletal models with the replaced biarticular muscles. All three new musculoskeletal designs predicted greater metabolic cost than the standard model. Analyzing the mechanisms proposed in the literature by which biarticular muscles might yield energy savings did not reveal a general cause for the increases. We conclude that the greater metabolic costs likely resulted from unique coordination patterns adopted by the altered musculoskeletal designs to meet the task demands of pedaling.

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