By Emmett Shaul
BLUF
A pilot study examined the effects of Alaska backcountry expeditionary hunting on skeletal muscle protein synthesis under conditions of physical and nutrient stress. The study found that despite significant negative energy balance and weight loss , participants maintained skeletal muscle mass. The study also found that muscle protein synthesis (MPS) increased despite negative energy balance, fractional synthetic rates (FSRs) of skeletal muscle proteins were elevated, and molecular markers such as myomiRNAs (miR-206, miR-23a-3p) and muscle genes (FSTL1) showed positive regulation of muscle plasticity.
Skeletal Muscle Protein Synthesis (MPS)
Skeletal muscle protein synthesis is the process by which the body builds new muscle proteins to repair, maintain, and grow skeletal muscle tissue. MPS occurs in response to exercise, dietary protein intake, and hormonal signals, and is a key driver of muscle growth, recovery, and adaptation.
Purpose of the Study
The study aimed to:
- Measure skeletal muscle protein synthesis using the novel virtual biopsy method during Alaska backcountry hunting.
- Evaluate molecular markers of muscle protein metabolism to understand muscle remodeling under negative energy balance.
- Explore implications for operational and tactical scenarios where physical resilience is critical under caloric deficit.
Subjects
The study included 4 participants:
- 2 Males (47 and 56 years old, BMI: 26.1 and 28.1 kg/m²)
- 2 Females (28 and 62 years old, BMI: 25.5 and 26.7 kg/m²)
- Age Range: 28 – 62 years (Mean = 48 ± 15 years)
- Body Mass Index (BMI): 26.6 ± 1.1 kg/m²
Clinical Characteristics and Body Composition:
- All participants experienced weight loss and reduction in fat mass:
- Mean Body Weight Loss: −2.1 ± 1.2 kg
- Fat Mass Reduction: −1.6 ± 0.2 kg
- Lean Tissue Mass: Maintained or slightly increased (+0.3 ± 1.0 kg)
Research Method
The study utilized a repeated measures, cross-sectional design:
- Field Setting: Conducted during two backcountry hunting expeditions in the Brooks Range of Alaska (13 days in 2019 and 8 days in 2020).
- Virtual Biopsy Method:
- Used isotopic labeling with deuterated water to measure the synthesis of skeletal muscle proteins.
- Blood and saliva samples were collected to calculate the Fractional Synthetic Rates (FSRs).
- Muscle Biopsy and Molecular Analysis:
- Muscle biopsies from the vastus lateralis were obtained before and after the expedition.
- Gene Expression Analysis: Real-time PCR evaluated muscle genes FSTL1, MEF2C, MYOD1, B2M.
- MicroRNA (myomiRNAs) Analysis: Examined miR-1-3p, miR-206, miR-208b-3p, miR-23a-3p, and miR499a-5p.
Findings
Muscle Protein Synthesis (MPS)
- Despite negative energy balance (−9.7 ± 3.4 MJ/d), muscle protein synthesis was elevated.
- Fractional Synthetic Rates (FSRs):
- Carbonic Anhydrase-3 (CA-3) FSR: 2.4 ± 1.8% per day
- Creatine Kinase M-type (CK-M) FSR: 4.0 ± 2.9% per day
- These FSRs exceeded those observed in younger adults following sprint interval training.
Molecular Markers of Muscle Remodeling
- Skeletal Muscle Gene Expression:
- FSTL1: Increased by ~3-fold, indicating positive regulation of muscle remodeling.
- MEF2C and MYOD1: Minimal changes observed.
- B2M: Slight decrease, indicating reduced inflammation.
- Skeletal Muscle MicroRNA (myomiRNAs):
- miR-23a-3p: Increased ~24-fold, linked to muscle growth and protein synthesis.
- miR-206: Increased ~5-fold, associated with muscle adaptation and plasticity.
Body Composition Changes
- Total Fat Mass Reduction: −1.6 ± 0.2 kg
- Lean Tissue Mass: Maintained or slightly increased (+0.3 ± 1.0 kg)
- Despite weight loss, participants preserved lean muscle mass, suggesting efficient muscle remodeling under caloric deficit.
Analysis and Implications
- Muscle Protein Synthesis under Physical and Nutrient Stress:
- The study demonstrated that sustained physical activity during Alaska backcountry hunting promoted muscle protein synthesis, even with significant caloric deficit.
- Movement constancy (continuous physical activity) likely stimulated muscle remodeling, preserving skeletal muscle mass.
- Molecular Mechanisms:
- Positive regulation of FSTL1 and miR-23a-3p supports the notion that muscle remodeling occurs under physical and nutrient stress.
- These molecular changes indicate muscle plasticity and adaptation to extreme environmental and physical conditions.
- Operational and Tactical Implications:
- Findings provide insights relevant to military training and operations, where energy deficit and movement constancy are common.
- Strategies can be developed to enhance physical resilience and muscle preservation during extended missions or endurance events.
Practical Applications
- Nutritional Strategies:
- Although negative energy balance was observed, muscle remodeling was supported by endogenous protein synthesis.
- High-protein diets or essential amino acid supplementation may further enhance muscle remodeling in similar operational environments.
- Training Recommendations:
- Incorporate movement constancy in endurance training programs to stimulate muscle plasticity and adaptation.
- Consider caloric deficit scenarios in training simulations to enhance resilience and metabolic efficiency.
- Operational Readiness:
- Military personnel can maintain muscle mass and performance during extended missions by leveraging movement constancy and strategic protein synthesis.
- This approach is relevant for tactical athletes operating in austere or calorie-deficient environments.
Conclusion
- The study demonstrates that Alaska backcountry expeditionary hunting promotes sustained muscle protein synthesis despite negative energy balance and physical stress.
- Positive regulation of muscle genes and myomiRNAs supports muscle remodeling and adaptation.
- Findings have operational implications for military personnel and practical applications for endurance athletes facing similar stressors.
- Further research is needed to explore the long-term effects of nutrient and physical stress on muscle protein synthesis and metabolic adaptation.
Bibliography
Coker, R.H., Ruby, B.C., Bartlett, L., Murphy, C.J., Priebe, K., Shriver, T.C., et al. (2023). Alaska Backcountry Expeditionary Hunting Promotes Sustained Muscle Protein Synthesis. Wilderness & Environmental Medicine, 34(3). DOI: 10.1016/j.wem.2023.05.003.