Muscle Response to Different Amounts of Dietary Protein During Leg Immobilization

The Effects of Varying Protein Intakes on Muscle Protein Synthesis During Injury-Mediated Muscle Disuse

Individuals who sustain musculoskeletal injuries (MSKI) can experience a rapid loss of muscle mass due to declines in muscle loading and activation that occur post-injury (i.e., disuse atrophy). Loss of muscle under these conditions is attributed to a persistent negative net muscle protein balance (muscle protein synthesis [MPS] < muscle protein breakdown) that results, in part, from declines in postprandial MPS (i.e., anabolic resistance). Nutritional interventions that enhance postprandial MPS may be used to overcome disuse-induced anabolic resistance and preserve muscle mass to accelerate recovery and improve recovery outcomes. While supplemental protein has been explored as a potential countermeasure to disuse-induce anabolic resistance, the observed efficacy of such interventions has been mixed. Equivocal findings across studies may be attributed, in part, to an insufficient understanding of what constitutes an effective protein-based intervention. Importantly, no study to date has determined an optimal protein dose for overcoming disuse-induce anabolic resistance, or if there is a threshold for maximally stimulating postprandial MPS under disuse conditions. Therefore, the objective of this work is to determine rates of MPS at rest and in response to standard (20 g) or high (40 g) doses of whey protein during knee immobilization (DISUSE) compared with standard activity (ACTIVE)

Study Overview

• Status: Recruiting
• Conditions: Muscle Disuse; Muscle Disuse Atrophy
• Intervention / Treatment: Dietary supplement: 20 grams protein; Dietary supplement: 40 grams protein

Detailed Description

Healthy, recreationally active men and women will complete this randomized, double-blind, parallel study. Muscle disuse will be implemented for five days using a unilateral leg immobilization model with one leg assigned to immobilization (DISUSE) and the contralateral leg used as a control (ACTIVE). Immobilization will be implemented with a rigid knee brace fixed at ~60° of flexion and participants will ambulate using crutches. Diets will be standardized during the immobilization phase. Participants will complete a protein feeding study at the end of immobilization consisting of primed, continuous stable isotope infusions, serial blood draws, and muscle biopsies. MPS will be assessed in both the DISUSE and ACTIVE legs in response to standard (20 g) or high (40 g) doses of whey protein. Findings from this work will directly inform the development of targeted nutritional countermeasures for overcoming disuse-induced anabolic resistance and preserving muscle mass after MSKI to optimize physical performance recovery.

• Study Type: Interventional
• Enrollment (Estimated): 28
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Emily E Howard, PhD; Phone Number: 508-206-2309; Email: emily.e.howard14.civ@health.mli

Study Locations

• United States
  • Massachusetts
    • Natick, Massachusetts, United States, 01760
      • Recruiting
      • US Army Research Institute of Environmental Medicine
      • Contact: Emily Howard, PhD; Phone Number: 508-206-2309; Email: emily.e.howard14.civ@health.mil
      • Principal Investigator: Emily E Howard, PhD

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Men and women aged 18-39 years (17-39 years if military personnel)
• Body mass index (BMI) between 18.5-32 kg/m2
• Routinely participate in aerobic and/or resistance exercise at least 2 days per week.
• Willing to refrain from alcohol, smoking, smokeless nicotine products (includes e-cigarettes, vaping, chewing tobacco), and dietary supplements (i.e., vitamin D, probiotics) 24 hours before and during immobilization and final testing day.
• Willing to only consume caffeine products provided by study staff during the study.
• Supervisor approval for federal civilian employees and non-SRV active-duty military personnel stationed at NSSC.
• Biological females must have normal menstrual cycles between 26-32 days in duration; 5 menstrual cycles within the past 6 months; or on continuous hormonal contraception (i.e., IUD or oral contraceptives without placebo).

Exclusion Criteria:

• Musculoskeletal injuries that may interfere with the safe use of crutches.
• Personal or family history of thrombosis, or prior diagnosis of deep vein thrombosis (DVT) or pulmonary embolism (PE).
• Metabolic or cardiovascular abnormalities, gastrointestinal disorders, neuromuscular disorders, lower-limb amputation, or muscle/bone wasting disorders (e.g., diabetes, cardiovascular disease, Crohn's disease, etc.).
• Taking medication that affects macronutrient utilization (i.e., statins, corticosteroids, weight loss medications such as Ozempic, etc.).
• Significantly abnormal blood clotting as determined by USARIEM Office of Medical Oversight (OMSO) or home duty station medical support (HMS).
• Allergy to lidocaine (or similar local anesthetic).
• Present condition of alcoholism, anabolic steroid use, or other substance abuse issues as determined by OMSO or HMS.
• Blood donation within 8-wk of beginning the study.
• Pregnant, trying to become pregnant, and/or breastfeeding (results of urine pregnancy test and self-report for breastfeeding will be obtained before body composition testing).
• Unwilling or unable to consume study diets or foods provided due to personal preference and/or food allergies.
• Unwilling or unable to adhere to study physical restrictions (i.e., no structured physical activity or recreational activity beyond activities of daily living) 24 hours before and during immobilization, and the final testing day.
• Unwilling or unable to keep the knee brace on and walk with crutches during the immobilization phase.

Study Plan

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Standard Protein Dose; Participants will consume 20 g of whey protein after 5 days of muscle disuse	Dietary supplement: 20 grams protein; 20 grams of whey protein provided as beverage
Active Comparator: High Protein Dose; Participants will consume 40 g of whey protein after 5 days of muscle disuse	Dietary supplement: 40 grams protein; 40 grams of whey protein provided as beverage

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Rates of postabsorptive and postprandial muscle protein synthesis assessed using 2H5-Phenylalanine stable isotope methodologies.	Postabsorptive and postprandial muscle protein synthesis in response to 20 or 40 g of whey protein determined using 2H5-Phenylalanine stable isotope methodologies and expressed as fractional synthetic rate (FSR).	After 5 days of muscle disuse

Collaborators and Investigators

• Sponsor: United States Army Research Institute of Environmental Medicine

Study record dates

Study Major Dates

• Study Start (Actual): September 1, 2025
• Primary Completion (Estimated): September 1, 2026
• Study Completion (Estimated): September 1, 2026

Study Registration Dates

• First Submitted: May 21, 2025
• First Submitted That Met QC Criteria: July 7, 2025
• First Posted (Actual): July 16, 2025

Study Record Updates

• Last Update Posted (Estimated): September 11, 2025
• Last Update Submitted That Met QC Criteria: September 4, 2025
• Last Verified: September 1, 2025

More Information

Terms related to this study

• Keywords: muscle protein synthesis; dose-response; immobilization; anabolic resistance; muscle disuse; muscle disuse atrophy
• Additional Relevant MeSH Terms: Musculoskeletal Diseases; Nervous System Diseases; Muscular Diseases; Neuromuscular Diseases; Muscular Disorders, Atrophic
• Other Study ID Numbers: 25-04H; MO240092 (Other Grant/Funding Number: MOMRP)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be shared.

Drug and device information, study documents

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