Muscle Protein Synthesis
Introduction[edit | edit source]
The plasticity of skeletal muscle is mediated, at least in part, by the constant turnover or remodeling of muscle proteins. Muscle protein synthesis (MPS) occurs at a fast rate when the body is growing and slows significantly after age 20.
- In healthy, recreationally active individuals, skeletal muscle proteins display turnover rates of ∼1.2% per day and exist in dynamic equilibrium.
- A combination of resistance exercise (RE), diet, and nutritional supplementation induces MPS
Key Facts[edit | edit source]
MPS is the driving force behind adaptive responses to exercise and represents a widely adopted proxy for gauging the chronic efficacy of acute interventions, (i.e. exercise/nutrition).
An acute exercise stimulus, especially resistance exercise, and protein ingestion both stimulate MPS and work in synergy when protein consumption occurs before or after resistance exercise.
- For building muscle mass and for maintaining muscle mass an overall daily protein intake in the range of 1.4–2.0 g protein/kg body weight/day (g/kg/d) is sufficient for people exercising.
- New evidence proposes that higher protein intakes (>3.0 g/kg/d) may have positive effects on body composition in resistance-trained individuals. That is it promotes the loss of fat mass.
- The ideal protein intake per serving for athletes to maximize MPS varies but common recommendations are 0.25 g of a high-quality protein per kg of body weight, or an absolute dose of 20–40 g. These protein doses should ideally be evenly distributed, every 3–4 h, across the day.
- Physically active individuals may obtain their daily protein requirements through the consumption of whole foods, supplementation is an option to ensure intake of adequate protein quality and quantity, without too many calories.
- Athletes should consider focusing on whole food sources of protein that contain all of the essential amino acids (EAAs) as they stimulate MPS. EEAs are required for normal health, and are either not manufactured in the body or manufactured in insufficient quantities. They are supplied by dietary protein and include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
- Pre-sleep casein protein intake (30–40 g) provides increases in overnight MPS and metabolic rate without influencing lipolysis. Casein is a protein found in milk and dairy products, accounting for roughly 80% of the protein in milk, cheese, and yogurt.
- The relationship between diet and protein balance is not straightforward. Even with increased protein intake, MPS is triggered for only a finite period of time. This is because the body can only utilize so much of the essential amino acids (EAAs) it receives; anything more will be broken down and excreted by the liver. However the anabolic effect of exercise is long-lasting (at least 24 h) but likely diminishes with increasing time post-exercise.
MPS And Immobility[edit | edit source]
This video explores immobility's impact on muscle protein synthesis and breakdown. It examines the muscle and strength loss from periods of immobility and the effect of amino acid supply on the rebuilding of muscle strength, mass, and function.
MPS and Resistance Exercise[edit | edit source]
Repeated bouts of resistance exercise (RE) lead to a persistent positive MPS balance, leading to the accumulation of contractile material (predominantly actin and myosin), and therefore muscle hypertrophy. With resistance exercise training (RET) these changes may become visible after just a few weeks of training, with gains typically decreasing as training advances. Adaptations to RE are influenced by the RE regime and nutritional sufficiency however with protein intake, the additional effect size is small.
Biological factors (such as DNA and sex), nutrition, and training variables can affect muscle hypertrophy. RE does not result in uniform growth responses between individuals, with large-ranging values reported, with many showing no hypertrophy responses to RET. Our understanding of this remains elusive.
Despite sizeable investment in pharmaceutical interventions and uncovering of a number of potential new targeted pharmaconutrients, RE with appropriate supportive nutrition is the current most effective and safe way to maintain or increase muscle mass in older adults, and address sarcopenia
MPS Physiologic Cascade[edit | edit source]
As can be seen below MPS is a physiologic cascade. The detailed diagram is of the molecular signaling cascades that are involved in myofibrillar MPS and mitochondrial biogenesis in response to RE and specific amino acids or their derivatives (primarily leucine and beta-hydroxy beta-methylbutyrate).
Abbreviations and schematic representations:
- PLD: phospholipase D
- PA: phosphatidic acid
- mTOR: mechanistic target of rapamycin (a central mediator of protein synthesis in skeletal muscle).
- AMP: adenosine monophosphate
- ATP: adenosine triphosphate
- AMPK: AMP-activated protein kinase
- PGC‐1α: peroxisome proliferator-activated receptor gamma coactivator-1α
- 4EBP1: eukaryotic translation initiation factor 4E-binding protein 1
- S6K1: p70S6 kinase
- eIF4E: eukaryotic translation initiation factor 4E
- RPS6: ribosomal protein S6
- eEF2: eukaryotic elongation factor 2
- RE: resistance exercise; EE: endurance exercise
- Myo: myofibrillar; Mito: mitochondrial
- AA: amino acids
- ↑ represents activation
- Τ represents inhibition
References[edit | edit source]
- Encylopedia Sports fitness Available from:https://www.encyclopedia.com/sports/sports-fitness-recreation-and-leisure-magazines/muscle-protein-synthesis (accessed 23 November 2022)
- Witard OC, Bannock L, Tipton KD. Making sense of muscle protein synthesis: a focus on muscle growth during resistance training. International journal of sport nutrition and exercise metabolism. 2021 Oct 25;1(aop):1-3.
- Atherton PJ, Smith K. Muscle protein synthesis in response to nutrition and exercise. The Journal of physiology. 2012 Mar 1;590(5):1049-57.
- GSK . GSK HPL Deep Science: Muscle Protein Synthesis. Available from: https://www.youtube.com/watch?v=uGc7nY2lgEM [last accessed 25.11.2022]
- Merriam webster EEAs Available from:https://www.merriam-webster.com/dictionary/essential%20amino%20acid (accessed 25 November 2022)
- Very well health Casein Available from:https://www.verywellhealth.com/casein-5081318 (accessed 25 November 2022)
- Jäger R, Kerksick CM, Campbell BI, Cribb PJ, Wells SD, Skwiat TM, et al. International society of sports nutrition position stand: protein and exercise. Journal of the International Society of Sports Nutrition. 2017 Jun 20;14(1):20.
- Young sub Kwon, M.S. and Len Kravitz, Ph.D. How do muscles grow? Available from:https://www.unm.edu/~lkravitz/Article%20folder/musclesgrowLK.html (accessed 25 November 2022)
- Brook MS, Wilkinson DJ, Phillips BE, Perez‐Schindler J, Philp A, Smith K, et al. Skeletal muscle homeostasis and plasticity in youth and ageing: impact of nutrition and exercise. Acta physiologica. 2016 Jan;216(1):15-41.