Graduation Year

2020

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts

Department

Biology

Reader 1

Jenna Monroy

Reader 2

Lars Schmitz

Abstract

This study focuses on training that promotes eccentric contraction, which is muscle activation during lengthening. Eccentric training is associated with hypertrophy and changing elastic properties of muscle. We hypothesize that eccentric training in mice will result in changes to the elastic properties of extensor digitorum longus (EDL) muscles, measured as elastic recoil, such that muscles that have undergone training will be less compliant than those that have not.

Twelve female mice were randomly separated into control and exercise groups; the exercise group underwent five weeks of eccentric training using a protocol of progressive overload, approved by Claremont Colleges IACUC. After five weeks EDL muscles were removed and elastic muscle properties were measured using load clamp tests in which muscles are activated isometrically or stretched passively to a known force after which muscle recoil is measured in response to a rapid decrease in load. Both the control and exercise muscles showed a significant increase in elastic modulus, the length at which force develops, and muscle stiffness upon activation; however, their compliance in response to activation varied.

There were two different responses to eccentric training: three EDL muscles significantly increased in stiffness in comparison to the control muscles while four did not. An increase in muscle stiffness with training may be associated with a change in the properties of the muscle protein titin. Titin is known to contribute to passive stiffness, but its role in active contraction remains largely unknown. Previous researchers have proposed that upon muscle activation, titin binds to actin, resulting in increased muscle stiffness. The data presented here suggest that muscle stiffness may increase in response to training with possible age-based effects, possibly due to changes in titin isoforms present in the sarcomere. Future work will investigate whether titin underlies these changes in muscle elastic properties.

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This thesis is restricted to the Claremont Colleges current faculty, students, and staff.

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