Amino Acids and Muscle Protein Synthesis
Muscle protein synthesis and deposition is a process that occurs in the body. It is stimulated by amino acids. However, the ability of skeletal muscle to accumulate protein is limited by inelastic collagen connective tissue. Therefore, muscle protein synthesis must be maintained by proper protein consumption. The amount of amino acids a person 단백질 쉐이크 consumes will determine how much muscle protein they produce.
Increased amino acid intake stimulates muscle protein synthesis
The effects of increased amino acid intake on muscle protein synthesis depend on the form and timing of amino acid ingestion and their interactions with other factors. Branched-chain amino acids activate key enzymes responsible for muscle protein synthesis after physical exercise. In a study published in 1981, Buse MG and Garlick PJ reported that branched-chain amino acid infusions triggered increased muscle protein synthesis and improved insulin sensitivity in fasted rats.
Recent in vitro studies have shown that amino acids are an important regulator of muscle protein synthesis. Using an arteriovenous balance approach and stable isotope methodology, scientists have quantified the effects of amino acid availability on MPS. They found that amino acid intake doubles the rate of MPS, but further increases in concentration were ineffective. In contrast, when amino acids are bolus-infused, MPS increases more rapidly and the peak rate is higher than during constant ingestion. Similarly, ingestion of nonessential amino acids inhibits muscle protein synthesis.
In addition, studies of increased amino acid intake in rats have shown that branched-chain amino acids suppress muscle proteolysis and stimulate muscle protein synthesis. In humans, protein synthesis and turnover are controlled by different mechanisms than in rats. In rat models, protein synthesis is inhibited by initiation, whereas the translation process is unrestricted in humans. Therefore, the effects of amino acids on muscle protein synthesis in humans are different from those observed in rats.
Limitation of muscle protein accretion by inelastic collagen connective tissue
Inelastic collagen connective tissue contains a matrix of protein fibers containing collagen and elastin. The muscle fibrogenic cells, however, are largely MyoD+. In addition, a proportion of these cells express Tcf4 immunocytochemically. Nevertheless, this association has been unclear. The current findings may point to the existence of an important mechanism that limits MPS.
Effects of age on muscle protein synthesis
We examined the effects of age on muscle protein synthesis in young and elderly men and women in the laboratory using a biochemical method called isotopically labeled amino acid. We found similar postabsorptive fractional synthesis rates in young and older adults across the mitochondrial and sarcoplasmic fractions. After resistance exercise, the rates of sarcoplasmic and mitochondrial synthesis significantly increased.
Age-related changes in muscle protein synthesis are associated with changes in several physiological processes. Aging can affect protein digestion, amino acid absorption, and microvascular perfusion. These changes may affect muscle mass and strength in older individuals. Moreover, aging can decrease the postprandial hormonal response and affect amino acid uptake.
Age-related changes in muscle protein synthesis may have a positive effect on exercise performance. In young and middle-aged adults, basal muscle protein synthesis is not affected by age. However, aging may affect basal levels of muscle protein synthesis in obese adults. This discrepancy could be related to the method used to measure basal synthesis. In the former study, plasma phenylalanine enrichment was used to measure muscle protein synthesis, which does not reflect the amino acid levels in muscle tissues.
Effects of protein quality on muscle protein anabolism
Several recent studies have examined the effect of protein quality on muscle protein anabolism. A higher-quality protein appears to promote greater muscle protein synthesis in the short term and longer-term, and it also reduces muscle protein breakdown. However, more research is needed to understand the precise effect of protein quality.
The amount of protein consumed plays an important role in muscle protein synthesis. Increasing the protein intake leads to an increase in MPS, which is necessary for hypertrophic gains. Moreover, protein intake leads to suppression of protein breakdown, which creates a net positive protein balance in the body. Leucine is a key amino acid that triggers the increase in MPS. Hence, ingested proteins with high leucine content are advantageous to increase MPS. The type of protein consumed is also relevant, since the quality of a protein can affect MPS and skeletal muscle mass.
In addition, protein quality can affect the acute post-exercise muscle protein synthetic response, which is crucial for muscle hypertrophy during resistance training. This review will explore the role of protein quality in muscle protein synthesis and skeletal muscle hypertrophy.