Logan Steele
Muscle synthesis, or muscle protein synthesis (MPS), is a metabolic process that produces muscle protein, facilitating the building and maintenance of muscle mass. It is the process by which amino acids are combined to form a complex chain, known as a protein. This amino acid chain is the primary structure of protein and the structural foundation of muscle. MPS is the driving force behind adaptive responses to exercise and is influenced by factors such as diet, nutrition, and training.
| Characteristics | Values |
|---|---|
| Definition | Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins. |
| Purpose | Muscle protein synthesis is important for building and maintaining muscle mass. |
| Factors | Muscle protein synthesis is influenced by training, diet, and nutritional supplementation. |
| Training | Resistance training, endurance training, and strength training can all stimulate muscle protein synthesis. |
| Diet | A sufficient intake of high-quality protein and essential amino acids, such as leucine, is necessary for muscle protein synthesis. |
| Protein Intake | Recommendations vary, but common suggestions include 0.83-2.0 g of protein per kg of body weight per day, with higher amounts potentially beneficial for older individuals or those engaging in resistance training. |
| Timing | Protein synthesis is increased after exercise, and consuming protein-rich foods during this time is important. It peaks 24 hours after a workout and gradually declines. |
| Measurement | The precursor-product method is commonly used to measure muscle protein synthesis rates, typically over a 3-12 hour period following exercise and/or nutrition stimulus. |
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What You'll Learn
Muscle protein synthesis and muscle breakdown
Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins. Muscle proteins can be classified into two types: contractile myofibrillar proteins (e.g. myosin, actin, tropomyosin, troponin) and energy-producing mitochondrial proteins. The synthesis of myofibrillar proteins is primarily responsible for changes in skeletal muscle mass following resistance training, while mitochondrial proteins are primarily synthesized in response to endurance-type training.
The plasticity of skeletal muscle is mediated by the constant turnover or remodelling of muscle proteins. MPS and muscle protein breakdown (MPB) are two metabolic processes that act concurrently to repair, replace, and generate new muscle proteins, leading to phenotypic adaptations. In healthy, recreationally active individuals, skeletal muscle proteins display turnover rates of about 1.2% per day and exist in dynamic equilibrium. In the fasted state, MPB exceeds MPS, while in the fed state, MPS exceeds MPB.
MPS is the driving force behind adaptive responses to exercise and is influenced by factors such as exercise mode, intensity, duration, and individual genetic makeup. Nutrient-driven increases in MPS are short-lived, lasting around 1.5 hours, and are further enhanced by resistance exercise, even up to 24 hours after a single exercise session. Endurance-type exercises like running or cycling also increase the synthesis of mixed muscle proteins, but these acute responses do not lead to significant changes in muscle mass.
MPB is an important metabolic component of muscle remodelling, adaptation to training, and increasing muscle mass. It involves the degradation of muscle proteins through the integration of three main systems: autophagy, and the calpain and ubiquitin-proteasome systems. While resistance exercise increases MPB, it does not match the increase in MPS. Various methods, such as stable isotope methodologies and proteomic analysis, are employed to measure MPS and MPB rates, providing insights into muscle growth and adaptation.
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The role of amino acids
Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins. The synthesis of myofibrillar proteins is primarily responsible for changes in skeletal muscle mass following resistance training, while mitochondrial proteins are primarily synthesized in response to endurance-type training.
Amino acids are the fundamental constituents of body proteins and serve as substrates for protein synthesis. Amino acids regulate protein synthesis in cell and animal models, but evidence for amino acids promoting protein synthesis in human muscles is less clear. Studies on the stimulation of human MPS by branched-chain amino acids (BCAAs) have been inconsistent. However, amino acids other than BCAAs, such as threonine and tryptophan, may also have MPS-stimulating effects.
The transmembrane transport of amino acids is the determinant of the availability of circulating essential amino acids (EAA) for protein synthesis. Maximal transport rates occur when EAA gradients between intra- and extracellular concentrations are large. By maximizing the EAA gradient, the rate-limiting step is no longer the supply of substrate (i.e., precursor amino acids) but rather the quantity of translational machinery (e.g., tRNA and ribosome content).
Ingesting protein-containing supplements and foods provides the EAA necessary to increase muscle and whole-body protein synthesis. Large variations exist in the EAA composition of supplements and foods, ranging from free-form amino acids to whole protein foods. A 100% increase in peripheral EAA concentrations increases the fractional synthesis rate (FSR) by ~34%.
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 hours across the day.
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Diet and nutrition
Muscle protein synthesis (MPS) is the process of building muscle protein. It is a complex topic that involves many factors, including nutrition and exercise.
Nutrition plays a crucial role in muscle protein synthesis. The type, timing, and amount of protein consumed are critical factors in promoting muscle protein synthesis. Dietary protein provides the essential amino acids needed for muscle protein synthesis. These amino acids are the building blocks of protein and are absorbed into the body through the food we eat. It is important to consume high-quality protein sources with complete amino acid profiles.
Studies have shown that milk proteins are more effective than soy proteins in promoting muscle protein synthesis. Whey protein, in particular, has been found to promote important cellular signaling changes and intramuscular accumulation of triglycerides while inhibiting hepatic fat accumulation. Carbohydrate consumption is also important, as it facilitates intracellular signaling through insulin and helps maintain the cell's energy status. However, it is worth noting that significant protein synthesis is unlikely with a carbohydrate-only supplement.
To maximize muscle protein synthesis, it is recommended to consume ten grams of essential amino acids or twenty-five grams of a complete protein before and after exercise. This can include plant-based protein sources such as pea protein, which provides the essential building blocks to support lean muscle mass and muscle recovery.
Additionally, resistance exercise (RE) plays a significant role in muscle protein synthesis. Studies have shown that repeated bouts of RE lead to a persistent positive MPS balance, resulting in muscle hypertrophy. The combination of RE and protein ingestion work synergistically to further stimulate MPS.
In summary, a diet rich in high-quality protein sources, essential amino acids, and whey protein can effectively promote muscle protein synthesis. Combining this with strategic carbohydrate consumption and resistance exercise can further enhance muscle growth and recovery.
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Exercise and training
Muscle protein synthesis (MPS) is a metabolic process that produces muscle protein, facilitating the maintenance or building of muscle mass. It works in opposition to muscle protein breakdown (MPB), which can accelerate the loss of muscle mass. MPS is the driving force behind adaptive responses to exercise and is influenced by both training and diet.
The intensity and duration of exercise also play a role in MPS stimulation. Higher-intensity exercises, such as strength training, can stimulate MPS for up to 72 hours, with a peak at 24 hours post-workout. Additionally, the mode of exercise, whether resistance or endurance training, can influence MPS responses. While resistance training is commonly associated with increased MPS, endurance-type exercises like running or cycling can also enhance mixed muscle protein synthesis.
Training each muscle group at least twice a week is recommended to optimise MPS. Consuming protein within a few hours after a workout is crucial due to its synergistic effect on MPS. Animal protein sources, such as whey protein, are recommended for their quick digestion and absorption, contributing to muscle recovery and maintenance. Distributing protein intake throughout the day, with a focus on consuming protein-rich meals after training, is an effective strategy to maximise MPS and stimulate muscle growth.
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Measuring muscle protein synthesis
Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins. The synthesis of myofibrillar proteins is primarily responsible for changes in skeletal muscle mass following resistance training, whereas mitochondrial proteins are primarily synthesized during endurance-type exercises such as running or cycling.
There are several methods to measure MPS, including the precursor-product method, which is the most common approach. This method involves administering stable isotope-labeled amino acids (e.g. 13C6 phenylalanine, 1–13C leucine) via intravenous infusion under controlled laboratory conditions. The incorporation of free amino acids into newly synthesized bound muscle proteins is then traced, typically over an acute period of 3-12 hours following a single exercise and/or nutrition stimulus.
Another technique for measuring MPS is the "flooding dose" or "large dose" technique, which involves administering a large dose of the tracee amino acid along with the tracer amino acid. The tracer is labeled with an isotope (radioactive or stable) of C, H, or N. The rate at which the labeled amino acid is incorporated into muscle protein reflects the rate of protein synthesis. This technique can be used to determine the synthesis rate of both constitutive and secreted proteins in any tissue and is suitable for any size animal.
Dynamic measures of muscle protein turnover can also be determined using stable isotope methodologies, which are non-radioactive and safe for use in humans. Stable isotopes are naturally occurring 'heavy atoms' that are essentially identical to their endogenous counterparts but can be distinguished by their mass difference using mass spectrometric techniques.
The measurement of MPS is important for understanding the adaptive responses of muscles to exercise and nutrition. It provides a proxy for gauging the chronic efficacy of acute interventions, such as exercise and nutrition. For example, studies have shown that nutrient-driven increases in MPS are of finite duration (approximately 1.5 hours), after which they switch off despite sustained amino acid availability. Additionally, the combination of resistance exercise and protein ingestion stimulates MPS and works synergistically when protein consumption occurs before or after resistance exercise.
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Frequently asked questions
Muscle synthesis is the metabolic process that produces muscle protein, facilitating the maintenance or building of muscle mass. It is also known as muscle protein synthesis (MPS).
Muscle synthesis occurs when amino acid chains are turned into muscle protein. This process is important because we are always experiencing some level of protein turnover, where muscle protein is either breaking down or building up.
Muscle synthesis can be increased by stimulating the muscles through training and ensuring a sufficient intake of good-quality protein through diet.
To optimise muscle synthesis, it is important to consume a sufficient amount of protein with all nine essential amino acids. This can be done through whole foods or supplements. Additionally, it is beneficial to time your protein intake around your workouts, as protein synthesis increases after exercise.
