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

Investigating the Impact of Micronized Progesterone on Skeletal Muscle Metabolism

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

Study Overview

• Status: Not yet recruiting
• Conditions: Healthy Volunteers; Female; Progesterone; Premenopausal
• Intervention / Treatment: Drug: Micronized progesterone (oral capsules); Drug: placebo capsule

Detailed Description

This is a single-site, randomized, double-blind, placebo-controlled Phase 1 clinical trial designed to evaluate the effects of micronized progesterone on exercise-induced skeletal muscle protein synthesis (MPS) in premenopausal women.

Participants will be healthy, naturally menstruating women aged 18-30 years. Each will be randomized to receive either two oral doses of micronized progesterone (400 mg total, administered as 2 × 200 mg capsules, 34 and 10 hours prior to testing) or a matched placebo.

During the infusion trial, participants will consume a standardized nutritional drink (~530 kcal; 22 g protein, 52 g carbohydrate, 26 g fat) and perform unilateral resistance exercise consisting of single-leg extensions (1 warm-up set followed by 4 working sets to volitional failure, 2-minute rest between sets).

To assess myofibrillar MPS, participants will undergo a primed continuous infusion of L-[ring-¹³C₆]-phenylalanine, with incorporation into muscle proteins determined from serial biopsies collected from both the exercised and rested legs. Blood samples will be obtained throughout the infusion period to measure plasma amino acids and hormone concentrations.

The primary endpoint is the treatment (placebo vs. progesterone) × leg (exercised vs. rested) interaction in MPS over the 5-hour post-exercise period. Secondary outcomes include the exercise-induced change in fractional synthetic rate (ΔFSR), plasma hormone responses, and exploratory measures of body composition and strength.

This study will provide direct evidence on whether progesterone modifies the acute anabolic response to resistance exercise in reproductive-age women, addressing an important gap in female skeletal muscle physiology.

• Study Type: Interventional
• Enrollment (Estimated): 20
• Phase: Phase 1

Contacts and Locations

• Study Contact: Name: Stuart Phillips, Ph.D.; Phone Number: 24465 905-525-9140; Email: phillis@mcmaster.ca

Study Locations

• Canada
  • Ontario
    • Hamilton, Ontario, Canada, L8S 4K1
      • Exercise Metabolism Research Laboratory
      • Contact: Stuart Phillips, Ph.D.; Phone Number: 24465 905-525-9140; Email: phillis@mcmaster.ca
      • Principal Investigator: Stuart Phillips, Ph.D.

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

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).

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Experimental: Micronized Progesterone; Drug - Micronized progesterone (oral capsules; 400 mg total as 2 × 200 mg at ~34 h and ~10 h pre-trial)	Drug: Micronized progesterone (oral capsules); Two doses of 400 mg total micronized progesterone, administered as 2 × 200 mg capsules ~34 hours and ~10 hours prior to infusion trial, taken with a standardized nutritional drink.; Other Names: PROMETRIUM
Placebo Comparator: Placebo Comparator: Placebo; Drug - Placebo (oral capsules; matched schedule and appearance)	Drug: placebo capsule; Matched oral placebo capsules administered on the same schedule (~34 and ~10 hours prior to infusion trial) with a standardized nutritional drink.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Myofibrillar muscle protein synthesis (MPS) rate	Incorporation of L-[ring-¹³C₆]-phenylalanine into myofibrillar proteins, measured via bilateral muscle biopsies (vastus lateralis, exercised vs. rested legs). The primary endpoint is the treatment (micronized progesterone vs. placebo) × leg (exercised vs. rested) interaction in MPS under fed conditions.	5 hours after standardized feeding and unilateral resistance exercise (infusion period)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Myofibrillar MPS in rested leg (fed condition)	MPS in the rested (non-exercised) leg to assess whether progesterone alters postprandial muscle anabolism in the absence of exercise.	5 hours after standardized feeding
Myofibrillar MPS in rested leg (fasted condition)	MPS calculated from baseline fasted blood/plasma enrichment and pre-meal biopsy to determine whether progesterone alters basal, fasted-state anabolism.	-240 to 0 minutes before feeding (fasted infusion period)
Circulating serum progesterone concentrations (pharmacokinetics)	Serial serum progesterone measured to characterize exposure; pharmacokinetic parameters include AUC, Cavg, Cmax, and Tmax.	-240 to 300 minutes (fasted and fed infusion periods)
Postprandial amino acid response	Serial serum amino acid concentrations (including essential and branched-chain amino acids) measured for PK parameters (AUC, Cavg, Cmax, Tmax) to contextualize MPS responses.	0 to 300 minutes after standardized feeding
Plasma tracer enrichment verification	Plasma enrichment of L-[ring-¹³C₆]-phenylalanine at steady-state timepoints to confirm validity of MPS calculations (target ≥2.0%).	Throughout infusion (-240 to 300 minutes)
Baseline menstrual phase and hormonal status	Baseline serum estradiol, LH, and FSH concentrations to verify early follicular phase timing and ensure group comparability.	Pre-dose (-240 minutes)

Collaborators and Investigators

• Sponsor: McMaster University

Study record dates

Study Major Dates

• Study Start (Estimated): September 15, 2025
• Primary Completion (Estimated): December 15, 2025
• Study Completion (Estimated): December 15, 2025

Study Registration Dates

• First Submitted: September 7, 2025
• First Submitted That Met QC Criteria: September 7, 2025
• First Posted (Estimated): September 15, 2025

Study Record Updates

• Last Update Posted (Estimated): September 25, 2025
• Last Update Submitted That Met QC Criteria: September 22, 2025
• Last Verified: September 1, 2025

More Information

Terms related to this study

• Keywords: Resistance exercise; Progesterone; Skeletal muscle; Muscle protein synthesis; Exercise metabolism; Female physiology; Stable isotope tracer; Premenopausal females; Micronized progesterone
• Additional Relevant MeSH Terms: Hormones; Hormones, Hormone Substitutes, and Hormone Antagonists; Polycyclic Compounds; Pregnanes; Steroids; Fused-Ring Compounds; Gonadal Steroid Hormones; Gonadal Hormones; Pregnenediones; Pregnenes; Corpus Luteum Hormones; Progesterone Congeners; Progesterone
• Other Study ID Numbers: MP4-MPS

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data (IPD) will not be shared due to the small sample size, the invasive nature of muscle biopsy procedures, and the risk of re-identification. Results will be disseminated in aggregate form through peer-reviewed publications and scientific presentations.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No