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Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins. It is the driving force behind adaptive responses to exercise and is influenced by the intensity of the workout, the type of exercise, and its duration. MPS is constantly occurring in the body, but exercise acts as a dimmer switch, increasing the rate at which it happens. The synthesis of myofibrillar proteins is primarily responsible for changes in skeletal muscle mass following resistance training, while mitochondrial proteins are primarily synthesized in endurance-type exercises. The rate of MPS decreases significantly after the age of 20, and specific amino acids and supplements have been shown to increase MPS in older individuals.
| Characteristics | Values |
|---|---|
| Definition | Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins. |
| Muscle Growth | Muscle hypertrophy (growth) occurs when muscle protein synthesis exceeds muscle protein breakdown. |
| Factors Influencing Muscle Growth | Exercise, nutrition, training status, training paradigms, genetics, and protein intake. |
| Protein Intake | An ideal protein intake to maximize MPS is 0.25 g of high-quality protein per kg of body weight or 20-40 g per serving. |
| Timing of Protein Intake | Faster MPS is linked to evenly distributed protein intake throughout the day, with recommendations of 25-40 grams every 3-4 hours. |
| Exercise Type | High-intensity exercises like bench pressing, deadlifting, interval training, and repeated hill climbs cause more muscle stress and a greater MPS response. |
| Exercise Timing | MPS is increased transiently after exercise and remains elevated for at least 24 hours, with potential visible changes after a few weeks of resistance training. |
| Age | MPS occurs at a faster rate during growth and slows significantly after age 20, with age-related muscle loss starting around age 50. |
| Measurement Methods | The precursor-product method is commonly used to determine muscle protein fractional synthesis rate (FSR) by tracing amino acid incorporation over 3-12 hours. |
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What You'll Learn
The metabolic process of muscle protein synthesis
Muscle protein synthesis (MPS) is a metabolic process that produces muscle protein, facilitating the maintenance or building of muscle mass. It is the process by which amino acids are incorporated into bound skeletal muscle proteins. Muscle proteins can be classified into 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 to produce energy.
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 about 1.2% per day and exist in dynamic equilibrium. This means that muscle protein breakdown (MPB) exceeds MPS in a fasted state, and MPS exceeds MPB in a fed state. In response to exercise, MPS is transiently increased, while MPB also increases or remains the same, provided there is a sufficient exogenous nutrient supply.
The intensity, type, and duration of exercise affect MPS. For instance, endurance-type exercises such as running or cycling are associated with increased synthesis of mixed muscle proteins. However, these acute responses are not associated with significant changes in muscle mass. On the other hand, repeated bouts of resistance exercise lead to a persistent positive MPS balance, resulting in the accumulation of contractile material and muscle hypertrophy.
Nutrition and protein intake also play a crucial role in MPS. Dietary protein provides the amino acids needed for muscle protein synthesis, and certain animal and plant-based protein sources offer a strong stimulus for MPS. For instance, soy protein and pea protein have been found to have high and balanced amino acid content. Additionally, specific amino acids like leucine, isoleucine, and valine have been shown to increase MPS and net balance, with leucine being particularly beneficial for older individuals experiencing age-related muscle loss.
Overall, MPS is a complex process influenced by various factors such as exercise, nutrition, genetics, and training status. By understanding and manipulating these factors, individuals can optimize MPS to achieve their desired fitness and health goals.
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The role of exercise in muscle protein synthesis
Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins. Skeletal muscles are highly plastic tissues that adapt to the metabolic demands of exercise. The plasticity of skeletal muscle is mediated by the constant remodelling of muscle proteins.
MPS is the driving force behind adaptive responses to exercise and is a widely used proxy for gauging the efficacy of acute interventions, such as exercise and nutrition. Exercise stimulates MPS, which works in synergy with protein ingestion, especially when protein consumption occurs before or after resistance exercise. The anabolic effect of exercise is long-lasting, lasting at least 24 hours, but likely diminishes with time post-exercise.
The synthesis of myofibrillar proteins is primarily responsible for changes in skeletal muscle mass following resistance training, whereas mitochondrial proteins are primarily synthesised in response to endurance-type training. Endurance exercises, such as running or cycling, are associated with increased synthesis of mixed muscle proteins, but not with significant changes in muscle mass. However, the amplitude of increase in mixed muscle MPS does not inform adaptation. For adaptation to be exercise-mode specific, there must be distinct responses of different protein fractions within the muscle.
The measurement of MPS is most commonly expressed as the rate of amino acid incorporation into bound muscle protein over a given time period, typically an hour or a day. The metabolic process of muscle protein breakdown describes the degradation of bound muscle proteins into their amino acid precursors, which occurs concurrently with MPS. The difference in rates of MPS and muscle protein breakdown determines whether muscle protein is gained or lost.
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The role of nutrition in muscle protein synthesis
Muscle protein synthesis (MPS) is a 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 synthesized in response to endurance-type training.
MPS is the driving force behind adaptive responses to exercise and nutrition interventions. It 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 about 1.2% per day and exist in dynamic equilibrium. In the fasted state, muscle protein breakdown (MPB) exceeds MPS, and in the fed state, MPS exceeds MPB.
Nutritional interventions that enhance MPS may be of great scientific and clinical interest as a strategy to promote positive muscle protein balance and eventual muscle protein accrual. The dose of dietary protein/essential amino acids (EAA) ingested, the protein food source, and the timing of protein consumption are all factors that influence MPS. For building and maintaining muscle mass, a daily protein intake of 1.4-2.0 g of protein per kg of body weight is sufficient for people exercising. However, higher protein intakes (>3.0 g/kg/day) may promote fat loss and have additional benefits for athletes.
The most common method for measuring MPS is the precursor-product method, which utilizes stable isotope-labeled amino acids to trace the incorporation of free amino acids into newly synthesized bound muscle proteins. This method is typically used over an acute 3-12 hour time period following an exercise and/or nutrition stimulus.
In summary, MPS is highly responsive to exercise and nutrition interventions, and nutritional strategies that enhance MPS may be valuable for individuals seeking to optimize muscle growth and performance.
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Measuring muscle protein synthesis
Muscle protein synthesis (MPS) is a popular topic in the fitness community. However, measuring it is a complicated process. The most common approach is the precursor-product method, which allows for the determination of muscle protein fractional synthesis rate (FSR). This method uses stable isotope-labelled amino acids (e.g. 13C6 phenylalanine, 1-13C leucine) administered intravenously under controlled laboratory conditions. The incorporation of free amino acids into newly synthesized bound muscle proteins is traced, typically over an acute 3–12-hour period following a single exercise and/or nutrition stimulus.
Another method for measuring MPS is the "flooding dose" technique, which uses L-[3H]-phenylalanine as a tracer. This method is suitable for determining the total and myofibrillar protein synthesis rate in skeletal muscle over a short acute period (less than 30 minutes) in any size animal. It involves administering the tracer without anesthesia and then collecting tissue and blood samples for analysis.
The majority of techniques for measuring MPS involve the use of amino acid tracers labelled with stable or radioactive isotopes of C, H, or N. The rate at which the labelled amino acid is incorporated into muscle protein is a function of the amount of labelled amino acid in the precursor pool at the site of translation, reflecting the rate of protein synthesis.
One alternative tracer that has been used successfully in mice, rats, fish, and humans is 2H2O, also known as deuterium oxide. This method, first described by Hans Ussing in 1941, involves providing 2H2O to the subject and measuring the rate of protein renewal by the incorporation of 2H atoms into the protein.
It is also possible to measure muscle protein synthesis by calculating nitrogen balance. Nitrogen balance is calculated as nitrogen intake minus nitrogen excretion, and a positive nitrogen balance indicates that the body is storing more protein than it is losing, suggesting an anabolic (growing) state.
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The impact of age on muscle protein synthesis
Muscle protein synthesis (MPS) is a metabolic process that involves the incorporation of amino acids into bound skeletal muscle proteins. This process is responsible for the growth and maintenance of muscle mass. MPS occurs rapidly when the body is growing and typically slows down significantly after the age of 20.
Age-related muscle wasting, also known as sarcopenia, is a condition characterised by a loss of muscle strength and function that commonly occurs with advancing age. This condition has been associated with a reduction in basal muscle protein synthesis rates, particularly in the synthesis of myosin heavy chain (MHC) protein, which is crucial for muscle contraction and energy production. Studies have shown that older individuals exhibit lower rates of mixed-muscle, MHC, and nonmyofibrillar protein synthesis compared to younger individuals.
However, the relationship between aging and muscle protein synthesis is complex and not yet fully understood. While some studies have demonstrated reduced postabsorptive muscle protein synthesis with age, others have failed to find a significant age effect. Additionally, it is important to consider the role of other factors such as nutrition, exercise, and hormonal influences, which can also impact MPS rates. For example, older muscles may become resistant to anabolic stimuli such as amino acids and resistance exercise, requiring higher quantities of protein to stimulate MPS effectively.
The rate of muscle loss with aging varies between men and women. Men generally experience a higher rate of muscle loss, but women tend to have smaller muscles throughout their lives. Additionally, obesity may play a role, as obese older women have been found to have higher basal muscle protein synthesis rates than their male counterparts.
To counteract age-related sarcopenia, interventions focusing on nutrition and exercise can be implemented. For instance, ensuring adequate protein intake and engaging in resistance exercises can stimulate MPS and potentially slow down the effects of aging on muscle synthesis. However, it is important to note that the responsiveness of MPS to these anabolic stimuli may diminish with age, and further research is needed to fully understand the complex interplay between aging and muscle protein synthesis.
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Frequently asked questions
Muscle protein synthesis (MPS) is a metabolic process that produces muscle protein, facilitating the maintenance or building of muscle mass.
MPS is the driving force behind adaptive responses to exercise and nutrition. It works in opposition to muscle protein breakdown (MPB), which can accelerate the loss of muscle mass.
MPS occurs when the body turns the protein consumed into new muscle protein. This process is influenced by factors such as exercise, nutrition, and genetics.
To increase MPS, one can focus on consuming high-quality protein sources with complete amino acid profiles, such as animal protein or plant-based proteins like soy and pea protein. Additionally, specific amino acids like leucine, isoleucine, and valine can support muscle maintenance and synthesis.
The recommended daily protein intake for building and maintaining muscle mass is 1.4-2.0 g of protein per kg of body weight. This can be distributed across meals and snacks throughout the day, with each meal containing approximately 25-40 grams of protein.
