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

Inclusion Criteria: 1. Self-identifies as female and is assigned female at birth. 2. Aged 18 to 30 years (inclusive). 3. Body mass index (BMI) between 18 and 34.9 kg/m² (inclusive). 4. In general, good health, as determined by a study-specific health screening questionnaire and medical history review. 5. Reports regular menstrual cycles (21-35 days in length) for the past 3 consecutive months. 6. Not currently using hormonal contraceptives and has completed a minimum 3-month washout period. 7. Resting blood pressure \<140/90 mmHg at screening and on the infusion day. 8. Willing and able to provide written informed consent in English. Exclusion Criteria: 1. Current use of tobacco, vaping products, or nicotine-containing substances. 2. Ineligible for physical activity as determined by the Get Active Questionnaire (GAQ). 3. Any medical, orthopedic, or psychiatric condition that, in the opinion of the Investigator, could interfere with the participant's ability to comply with study procedures or pose additional risk. 4. Current gastrointestinal or swallowing disorders that may interfere with supplement ingestion (e.g., chronic diarrhea, regurgitation, dysphagia). 5. Currently pregnant, planning to become pregnant, or known/suspected to be pregnant. 6. Use of hormonal contraceptives within the past 3 months. 7. Presence of any electronic medical devices or metallic implants that may interfere with DXA scanning or muscle biopsy procedures. 8. History of neuromuscular disorders or muscle/bone wasting diseases. 9. Current or recent use (within 3 months) of medications known to affect protein metabolism (e.g., glucocorticoids, systemic NSAIDs, isotretinoin, or anabolic agents). 10. Personal or first-degree family history of thrombotic events (e.g., DVT, PE, stroke, myocardial infarction). 11. Use of anticoagulant or antiplatelet medications. 12. Excessive alcohol intake (\>21 units per week; 1 unit = 10 mL of pure ethanol). 13. History of bleeding disorders or known coagulation or platelet abnormalities. 14. Known hypersensitivity or allergy to micronized progesterone, soya, peanuts, or any excipients in the study capsule. 15. History or current diagnosis of liver dysfunction or hepatic disease, unless liver function tests have returned to normal ranges. 16. History or presence of contraindications to progesterone therapy, including any of the following: 1. Known or suspected estrogen- or progestin-dependent malignancies (e.g., breast or endometrial cancer). 2. History of endometrial hyperplasia or unexplained abnormal uterine bleeding. 3. Active or prior history of arterial thromboembolic disease (e.g., stroke, myocardial infarction, coronary artery disease). 4. History of classical migraine with aura. 5. Active or prior history of venous thromboembolism (e.g., deep vein thrombosis, pulmonary embolism) or thrombophlebitis. 6. History of partial or complete vision loss due to ophthalmic vascular events. 17. Clinically significant anemia or hematologic abnormalities (e.g., low hemoglobin or hematocrit) that may elevate the risk of biopsy complications. 18. Participation in another interventional study involving investigational drugs or invasive procedures within the past 30 days. 19. Documented history of severe vasovagal syncope or needle phobia that may interfere with study compliance or safety. 20. Known allergy or intolerance to any ingredient in the BOOST® 2.24 nutritional drink (e.g., milk protein, soy, corn-derived ingredients, cocoa, or artificial flavorings).