Muscle has always been recognized for its importance in mobility and physical activity, and currently, there is a newfound appreciation for the importance of maintaining muscle for better health outcomes.
Before we proceed, let’s get comfortable with some key muscle terminology.
The process of building muscles (anabolism) is called muscle protein synthesis and the process of breaking down muscle (catabolism) is called muscle protein breakdown. Muscle protein turnover refers to the cycle of muscle being made and broken down.
Here’s where amino acid knowledge comes into play. Amino acids are the building blocks of the protein that makes up muscle. During muscle protein turnover, amino acids are released from muscle to be used as needed by other organs and tissues when there is not a plentiful supply of amino acids coming from your diet.
Muscle can be thought of as the main reservoir of amino acids for the body. In combination with a high-protein diet and/or amino acid and protein supplementation, weight training usually increases both muscle mass and strength. So, muscle health comes down to three key components:
- A high-protein diet
- Essential amino acid supplementation
- Regular weight training
Anabolic and Catabolic Stimuli
When we refer to anabolic stimuli, we are talking about factors and lifestyle choices that promote the growth or synthesis of new muscle. These include…
- Dietary protein intake
- Exercise—particularly resistance or weight-bearing exercise
- Anabolic hormones—like growth hormone and testosterone
We know for certain that amino acids, particularly essential amino acids, stimulate the growth of new proteins.
Factors that are catabolic, or promote muscle breakdown and loss, include…
- Low-protein diets
- Low-energy diets
- Illness and stress
During times of illness and stress, we have an increased need for amino acids to support immune system function and the action of catabolic hormones that are released in response to stress.
A Quick Lesson on Amino Acids and Muscle Protein
Muscles are made up of individual fibers constructed of proteins, and these proteins are made up of amino acids.
Amino acids are derived from dietary protein. Also, the body is capable of synthesizing certain amino acids through chemical reactions that occur in the liver and select sites throughout the body.
The amino acids that must be obtained from the diet are called essential amino acids (EAAs). Amino acids that can be made in the body are called nonessential amino acids.
The Production of New Muscle Protein
Muscle proteins are assembled from amino acids using information encoded in our genetic material—deoxyribonucleic acid (DNA). The sequence of amino acids in a protein is unique and distinguishes one protein from another. For protein synthesis to occur, all 20 “proteinogenic” amino acids must be present.
Ribonucleic acid (RNA) is the nucleic acid that carries instructions from the nuclear DNA into the part of the cell where protein is synthesized. Another type of RNA is transfer RNA (tRNA). Transfer RNA carries amino acids to the proper site for protein synthesis. When protein synthesis is taking place, enzymes link tRNA molecules to amino acids in a highly specific manner.
Transcription is one of the first processes to occur in protein synthesis, and it is basically the making of the RNA strands that carry the genetic code. The genetic code is transferred to an amino acid sequence in a protein through the translation process. The amino acids carried by tRNA molecules are positioned sequentially and linked together. One by one, amino acids are added to the growing chain until a stop signal is received. After the protein has been synthesized completely, it is removed from the cell structure that makes the protein for further processing and to perform its function.
A simple, conceptual way to think about muscle protein synthesis is to compare it to the construction of a building. The DNA is basically the idea for the design of the building. The RNA is the written plan or blueprint, and transcription is the process of writing up the plan. The charged tRNA and the process of translation, meaning tRNA plus its amino acid, is the construction company that builds the product by “putting the bricks together.” The protein is the final product or completed building ready to serve its function.
There are many detailed molecular studies of all the independent steps along these complicated biochemical pathways of muscle growth and breakdown, but these don’t always predict what will be observed in free-living human beings. For example, mRNA may be produced to initiate protein synthesis but if amino acids are not available, the protein cannot be made.
What’s the Deal with Muscle Protein Breakdown?
It is easy to understand the importance of muscle protein synthesis, as that is the metabolic basis for building muscle. But why do muscles need to be broken down as part of muscle protein turnover?
We’ve already learned that muscle protein breakdown is essential in the time between meals when other important tissues and organs need a constant supply of essential amino acids. Muscle protein breakdown also helps improve muscle function.
Muscle fibers become damaged during exercise and do not generate the same contractile force as new fibers. In steps muscle protein turnover to get rid of the older, damaged fibers (protein breakdown) and replace them with new, better-functioning fibers (protein synthesis). Accelerated muscle protein turnover can improve athletic training, even if total muscle mass does not change. A heavy workout induces local inflammation due to the damaged muscle fibers—the more rapid the muscle turnover, the more quickly the post-exercise inflammation will subside.
Amino Acids and Muscle
Essential amino acids are the most potent stimulators of muscle protein turnover. Without an adequate supply of essential amino acids, muscle protein turnover is limited because there are not enough essential aminos to maintain muscle protein synthesis at an accelerated rate.
In order to stimulate muscle protein turnover, you must get your essential amino acids from your diet since they can’t be produced in the body. It’s difficult to get an ample amount of essential amino acids from food alone, which is where a balanced essential amino acid supplement can come in handy.
Essential amino acid supplements can help improve muscle function without increasing muscle mass if that is your goal. For example, an endurance runner will improve muscle function and decrease inflammation by consuming essential amino acids after a workout without adding extra muscle weight. But, if your goal is to gain muscle mass, then supplementing with an essential amino acid powder is also a must. To build muscle, you will want to consume essential aminos with sufficient non-protein calories to add to the extra mass.