Progesterone and Muscle Protein Synthesis in Premenopausal Women (MP4-MPS)

The goal of this clinical trial is to learn if micronized progesterone (PROMETRIUM®) influences the muscle-building response to resistance exercise in healthy premenopausal women aged 18-30 years. The main questions it aims to answer are: 1. Does progesterone change the rate of muscle protein synthesis after exercise? 2. Does progesterone alter the difference in synthesis between an exercised leg and a rested leg? Researchers will compare micronized progesterone to a placebo to see if progesterone changes the way skeletal muscle adapts to resistance exercise. Participants will: * Take two oral doses of progesterone (400 mg total, 34 and 10 hours before testing) or placebo * Complete a unilateral leg extension exercise session in the lab * Receive an infusion of a stable isotope tracer and provide blood samples * Undergo muscle biopsies from the exercised and rested legs