Understanding Muscle Growth

Amino acids are the building blocks of all the proteins found in the human body. There are twenty different naturally occurring amino acids, and our genetic code determines their specific sequence and resulting chemical structure. Supplementation of certain amino acids have been consistently shown to influence growth of muscle tissue following a strenuous weight lifting routine. Both professional and amateur weightlifters alike have been consistently trying to adapt their exercise programs to maximise their muscular gains in the gym; however many underestimate the importance of a balanced diet as well as the use of such supplements.

There are three different types of muscle fibres found within the human body, each with varying structure and function.

The walls of the heart are composed of striated cardiac muscle tissue, made up of cardiomyocyte cells. These individual cells are connected through gap junctions, allowing electrical nerve impulses to travel in a co-ordinated wave-like fashion throughout both the atria and ventricles, in order to effectively eject blood from the heart chambers into the main systemic arteries.

Cardiac muscle is entirely controlled by the autonomic nervous system, meaning that it is subconsciously moderated by a range of internal receptors which detect changes in temperature, blood pH, and blood hormone levels.
Similar to cardiac muscle, smooth muscle is innervated by the autonomic nervous system and serves the primary function of regulating systemic blood pressure as well as helping food pass smoothly through the digestive tract by ensuring peristaltic contraction.
The third type of muscular fibre, comprising 40% of an average adult human’s body weight1, is skeletal muscle. Skeletal muscle is a type of striated muscle which is innervated by the somatic nervous system, allowing it to be controlled by nerve impulses from the cerebral cortex.

 

By contraction and shortening of these muscle fibres, we are able to flex and move all the major limbs of the body. Unlike smooth and cardiac muscle, skeletal muscles receive impulses from the corticospinal tracts of the descending motor nerves, meaning that they are entirely under conscious and voluntary control.

Each muscle cell is made up of a large number of contractile units known as sarcomeres, which consist of myofilaments called actin and myosin. A single skeletal muscle cell can contain over 100,000 sarcomeres2. In a rested muscle, the binding site on the actin filament for the myosin head is blocked by a protein called tropomyosin. When a nerve impulse arrives at a neuromuscular junction, intracellular calcium is released from the sarcoplasmic reticulum of muscle cells. These calcium ions bind to another protein known as troponin, which causes conformational changes that pull the tropomyosin protein out of the myosin binding site. The myosin head then hydrolyses ATP, and using the energy generated from this, binds to the actin filament and pulls it in a rowing motion. This is what causes contraction and shortening of the muscle fibre, which allows us to move major joints, such as the elbow joint using the biceps brachii muscle.

During the period following a bout of intense weight training, skeletal muscles are put into a state of overload, and in the presence of several hormones, are able to grow back larger and stronger than before. Muscle cells naturally contain a limited number of nuclei, and an increase in muscle size requires an increase in protein synthesis which originates in the cell nucleus. Therefore they need to increase the “myonuclei” number in order to synthesise new actin and myosin filaments.

Satellite cells

Surrounding muscle fibres there are a specific type of stem cells called satellite cells, which proliferate, differentiate and donate their nuclei to muscle cells damaged during weight training. As well as this, persistent tension on skeletal muscles causes damage to the cell walls of muscle fibres, which stimulates the release of hormones such as IGF-1, Human Growth Hormone (HGH) and testosterone 3 With an increased number of nuclei, muscle cells are able to utilise these anabolic hormones and grow to an increase size and strength than before the workout. This entire process of cellular microtrauma and subsequent overcompensation takes around 36-48 hours4 to complete.

BCAA’s & Muscle Recovery

The process of muscle recovery following an intense weight training session can be assisted through the use of a range of supplements including essential amino acids. An important consideration when taking these amino acids are their Bio-availability, that is, the efficiency of delivery to damaged muscle tissues. Specific amino acids which have been scientifically proven to assist muscle growth are known as Branched Chain Amino Acids, or BCAAs. These derive their name from their unique chemical structure, composed of a main protein chain which has a number of functional “tree like” branches. Isoleucine, Leucine and Valine are the three major BCAAs which are commonly used as supplements by fitness enthusiasts and bodybuilders. These reportedly constitute around one third of muscle protein.5 BCAAs function as nitrogen carriers, as well as stimulating production of insulin.

After a workout, muscle cells require glucose in order to produce ATP required for energy. Insulin, synthesised and released from the pancreas, causes integration of GLUT-4 glucose transporters into the cell membranes of muscle cells, allowing glucose to be moved into muscles and used as an energy source. Both leucine and isoleucine have been shown to demonstrate this effect6 . As well as boosting glucose uptake, BCAAs are an effective anabolic stimulant, aiding in combining smaller amino acids into complete protein structures that facilitate muscle growth.

 

Taurine is an amino acid which helps expand muscle cells and allow them to hold a greater volume of water. This can increase hydration which directly boosts protein synthesis, and also increases visual muscle fullness. 
The use of Arginine is reported to increase intramuscular nitric oxide levels, which dilate blood vessels and direct blood flow to nutrient deprived muscle tissue. It is also an important component in the production of growth hormone, and oral supplementation of 5-9 grams of arginine has shown to considerable increase resting growth hormone levels in the body7
Another compound which can increase the oxidation of fat and result in effective weight loss whilst maintaining lean muscle is Carnitine. The important of this amino acid is clear. The Carnitine shuttle (formally known as Carnitine-acylcarnitine translocase), present in the membranes of cell mitochondria, is responsible for transporting long chains of fatty acids into mitochondria, where they can then enter the Krebs Cycle and be used to produce energy in the form of ATP.

Opinions vary, but between 2-10g a day of carnitine is reported to have noticeable effects on fat burning as well as maintenance of lean muscle tissue, depending on the particular study. Furthermore, cholesterol levels can also be kept in check through its use. Finally, Beta-Alanine taken at doses of around 4g a day, especially in combination with creatine, can yield increases in both muscle size as well as performance8.

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Studies throughout the fitness community have shown amino acids to be highly important components of any weight lifters diet or supplementation program. Yielding noticeable increases in muscular size, strength and performance, they are undoubtedly worth considering if you wish to maximise the results from your work in the gym.

Studies have even shown that amino acid supplementation can increase lean body mass, leg strength, grip strength and walking performance in elderly patients suffering from sarcopenia, or degenerative loss of skeletal muscle mass9. This shows even more promise for the use of amino acids as supplements in people of all ages and physical condition.

  1. “The Muscular System” – http://library.thinkquest.org/06aug/01768/Muscular.html”
  2. Qutayba Hamid, Joanne Shannon, M.D., “Physiologic Basis of Respiratory Disease”, pg. 689.
  3. Kraemer, W. J., & Ratamess, N. A. (2005). “Hormonal responses and adaptations to resistance exercise and training.” Sports Medicine, 35, 339-361.
  4. “Muscle Growth Part 1: The Science Behind Why, And How, Does A Muscle Grow And Get Stronger?” http://www.simplyshredded.com/muscle-growth-part-1-the-science-behind-why-and-how-does-a-muscle-grow-and-get-stronger.html
  5. Goto, Masaru; Miyahara, Ikuko; Hayashi, Hideyuki., Crystal Structures of Branced-Chain Amino Acid Aminotransfease Complexed with Glutamate and Glutarate: True Reaction Intermediate and Double Substrate Recognition of the Enzyme. Biochemistry (American Chemical Society) v. 42 no. 14 (April 8 2003) p. 3725-33.
  6. “Isoleucine, a blood glucose-lowering amino acid, increases glucose uptake in rat skeletal muscle in the absence of increases in AMP-activated protein kinase activity.” – Journal of Nutrition, Sept 2005, 135(9):2103-8.
  7. “Growth hormone, arginine and exercise.” Current opinion in Clinical Nutrition and Metabolic Care, 2008 Jan;11(1):50-4.
  8. “A Beta-Alanine Study”, Journal of Strength and Conditioning Research 2011 Jul;25(7):1804-15.
  9. “Potential Application of Essential Amino Acid Supplementation to Treat Sarcopenia in Elderly People”, The Journal of Clinical Endocrinology and Metabolism, 2009 May; 94(5): 1524–1526.