Menstrual Cycle vs. Oral Contraceptives: Effects on Muscle Protein Metabolism After Resistance Exercise
NCT ID: NCT07258576
Last Updated: 2025-12-02
Study Results
The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.
Basic Information
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RECRUITING
NA
20 participants
INTERVENTIONAL
2025-07-20
2026-09-01
Brief Summary
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Despite its importance, females have historically been underrepresented in protein metabolism research. A long-standing assumption has been that fluctuations in female sex hormones such as estrogen and progesterone, whether across the natural menstrual cycle or in individuals using oral contraceptives (OCs), make metabolism and training responses too variable to study. Because of this, many researchers have excluded female participants for logistical reasons.
Resistance exercise, such as weightlifting, is the most effective way to increase muscle size and strength. Each resistance-training session triggers muscle protein synthesis (MPS), the process by which new muscle proteins are built. Consuming dietary protein or individual amino acids further increases the rate at which new proteins are formed. Over time, higher rates of protein synthesis support muscle growth and the maintenance of other lean tissues in the body.
The purpose of this study is to examine how menstrual cycle phases and OC use influence the synthesis of proteins in both muscle tissue and the rest of the body. Improving scientific understanding in this area will support more effective, evidence-based training and nutrition recommendations for females.
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Detailed Description
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Conditions
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Study Design
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RANDOMIZED
CROSSOVER
BASIC_SCIENCE
NONE
Study Groups
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Mid-Luteal Phase
5-9 days post-ovulation
Protein Beverage
Participants will consume 16 half-hourly (8 hours) isoenergetic, isonitrogenous beverages containing 1.2 g/kg/d protein.
Stable Isotope Tracer [D5]phenylalanine
Protein beverages will be enriched with the stable isotope \[D5\]phenylalanine. The use of \[D5\]phenylalanine will allow for determination of muscle protein synthesis.
Stable Isotope Tracer [13C]phenylalanine
Protein beverages will be enriched with the stable isotope tracer \[13C\]phenylalanine. The use of \[13C\]phenylalanine will allow for the determination of the fate of amino acids in the body (incorporation into body protein or oxidation) which can be used to determine protein requirements.
Early Follicular Phase
Days 2-6 post-menses onset
Protein Beverage
Participants will consume 16 half-hourly (8 hours) isoenergetic, isonitrogenous beverages containing 1.2 g/kg/d protein.
Stable Isotope Tracer [D5]phenylalanine
Protein beverages will be enriched with the stable isotope \[D5\]phenylalanine. The use of \[D5\]phenylalanine will allow for determination of muscle protein synthesis.
Stable Isotope Tracer [13C]phenylalanine
Protein beverages will be enriched with the stable isotope tracer \[13C\]phenylalanine. The use of \[13C\]phenylalanine will allow for the determination of the fate of amino acids in the body (incorporation into body protein or oxidation) which can be used to determine protein requirements.
Active Pill Phase
Days 10-20 of active pill
Protein Beverage
Participants will consume 16 half-hourly (8 hours) isoenergetic, isonitrogenous beverages containing 1.2 g/kg/d protein.
Stable Isotope Tracer [D5]phenylalanine
Protein beverages will be enriched with the stable isotope \[D5\]phenylalanine. The use of \[D5\]phenylalanine will allow for determination of muscle protein synthesis.
Stable Isotope Tracer [13C]phenylalanine
Protein beverages will be enriched with the stable isotope tracer \[13C\]phenylalanine. The use of \[13C\]phenylalanine will allow for the determination of the fate of amino acids in the body (incorporation into body protein or oxidation) which can be used to determine protein requirements.
Placebo Pill Phase
At least 48h after last active pill is taken
Protein Beverage
Participants will consume 16 half-hourly (8 hours) isoenergetic, isonitrogenous beverages containing 1.2 g/kg/d protein.
Stable Isotope Tracer [D5]phenylalanine
Protein beverages will be enriched with the stable isotope \[D5\]phenylalanine. The use of \[D5\]phenylalanine will allow for determination of muscle protein synthesis.
Stable Isotope Tracer [13C]phenylalanine
Protein beverages will be enriched with the stable isotope tracer \[13C\]phenylalanine. The use of \[13C\]phenylalanine will allow for the determination of the fate of amino acids in the body (incorporation into body protein or oxidation) which can be used to determine protein requirements.
Interventions
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Protein Beverage
Participants will consume 16 half-hourly (8 hours) isoenergetic, isonitrogenous beverages containing 1.2 g/kg/d protein.
Stable Isotope Tracer [D5]phenylalanine
Protein beverages will be enriched with the stable isotope \[D5\]phenylalanine. The use of \[D5\]phenylalanine will allow for determination of muscle protein synthesis.
Stable Isotope Tracer [13C]phenylalanine
Protein beverages will be enriched with the stable isotope tracer \[13C\]phenylalanine. The use of \[13C\]phenylalanine will allow for the determination of the fate of amino acids in the body (incorporation into body protein or oxidation) which can be used to determine protein requirements.
Eligibility Criteria
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Inclusion Criteria
* BMI between 18.5-29.9 kg/m2 (non-obese)
* Recreationally active (resistance train minimum twice a week)
* Using monophasic or triphasic oral contraceptives for \>1 year (for oral contraceptive users)
* Have regular menstrual cycles (21-35 days) for the past 3 months and discontinued any hormonal contraceptive use for at least 6 months (non-oral contraceptive users)
* Must meet a progesterone sufficiency test (non-oral contraceptive users)
Exclusion Criteria
* Chronic disease diagnosis (cardiovascular, thyroid, diabetes)
* Current or recent remission of cancer
* Regular use of non-steroidal anti-inflammatory drugs (NSAIDs; except low-dose aspirin), anticoagulants
* Use of prescription drugs that would impact muscle protein synthesis, e.g. Statins, Lithium, ADHD medication.
* Insertion of intrauterine device (IUD) - exception: copper
* Use of emergency contraception in the last 3 months (e.g. Plan B)
* Severe food allergies (e.g. soy, nuts)
* Smoking, use of performance enhancing drugs (growth hormones, testosterone)
18 Years
40 Years
FEMALE
Yes
Sponsors
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University of Toronto
OTHER
Responsible Party
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Daniel Moore
Associate Professor
Locations
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Goldring Center for High Performance Sport
Toronto, Ontario, Canada
Countries
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Central Contacts
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Facility Contacts
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Other Identifiers
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MCOC - REB00048059
Identifier Type: -
Identifier Source: org_study_id
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