Mammalian pregnancy brings large-scale physiological changes to the entire body. The body changes in composition, size and shape while the blood concentration of endocrine hormones surges. All of these changes have the potential to affect the remodeling and hence function of skeletal muscle. Yet, surprisingly little data exist about what happens during pregnancy to the muscles that now need to move an even heavier body carrying a large physiological investment: the fetus. Without this information clinicians cannot make evidence-based recommendations for exercise during pregnancy and the during the postpartum period. Using rats as a mammalian model system, we focus on the gastrocnemius muscle to begin to examine this overlooked part of female anatomy and physiology. Our project has four aims: