Graduation Year

2026

Document Type

Campus Only Senior Thesis

Department

Neuroscience

Reader 1

Jenna Monroy

Reader 2

Melissa Coleman

Abstract

Throughout pregnancy and lactation, fluctuations in hormones substantially alter the physiology of women’s bodies, but their effects on the musculoskeletal system remain largely understudied. Most existing work examines these changes from a histological perspective (Danos et al., 2023). Based on what is known about estrogen, relaxin, and other reproductive hormones, we expected that hormone fluctuations during pregnancy could shift muscles from slow oxidative (Type I) fibers toward faster glycolytic (Type IIa) fibers, and that the drop in estrogen during lactation would shift muscles back toward slower-twitch characteristics.

In this study, we examined these potential shifts from a physiological standpoint to determine whether muscle behavior aligns with what is known from histology. Soleus muscles were isolated from virgin, pregnant, and lactating C57BL/6 mice and tested in vitro using twitch and tetanic contractions to measure stress values, contraction rates, and relaxation rates. Understanding muscle behavior physiologically adds to the existing literature on hormonal influences on fiber-type transitions. These findings help clarify how pregnancy and lactation shape muscle function and contribute to further research on changes in metabolism and physical performance across reproductive states.

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

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