Effect of Branched-Chain Amino Acids on Muscle Breakdown & Repair

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Valine, leucine, and isoleucine make up the three amino acids known as branched-chain amino acids (BCAAs). BCAAs are critical to animal development and tissue synthesis, and are primarily found in plant sources in the animal diet. [1]

These three amino acids are part of the essential amino acids. This means that either our bodies cannot produce them, or that they cannot be produced in sufficient amounts in the body. Thus, they must be obtained through the diet. Humans cannot produce BCAAs, even in insufficient amounts and must get them through the diet. [1]

With the current research on genetically modified organisms (GMOs), there has been a lot of effort towards producing plants with higher concentrations of BCAAs. [1] Parallel to this research is the idea that with so much emphasis on athletic performance in today’s sports, increasing the nutritional value of foods could be a huge breakthrough and perhaps make healthier food options cheaper and more obtainable to athletes.

BCAAs have hit the market recently as an ergogenic aid used by athletes to speed up recovery by increasing muscle synthesis. Though they play a direct role in tissue synthesis in animals, is more really better?

What Makes BCAAs Stand Out

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With 20 amino acids playing such critical roles in the body, what makes BCAAs stand out above all others when it comes to protein ingestion and recovery from exercise? Is increasing physical activity linked to a utilization of more BCAAs in the tissue? These are the questions that have been considered for research on BCAAs.

Exercise activates the catabolism of BCAAs. When you begin exercising and causing strain on the muscle tissue, BCAAs begin to be catabolized and are depleted. This is controlled by the branched-chain α-keto acid dehydrogenase complex (BCKDH).

Essentially, exercise turns this complex on in skeletal muscle. [4] The BCKDH complex in skeletal muscle during resting conditions is in an inactive/phosphorylated state. This contributes to muscle growth and protein synthesis. [4]

Tissues are repaired during rest and recovery, because the complex inducing BCAA catabolism has been inactivated. Exercise, thus accelerates the rate of BCAA oxidation and protein degradation while decreasing the ability of the body to repair tissue damage. [2]

There is a distinct drop in BCAA levels in the body following exercise, primarily leucine. [2] This increases the need for BCAAs through diet and perhaps supplementation. [4]

Ingestion of BCAAs will increase tissue levels of leucine. [2] Leucine levels play a key role in the release of the initiation factor 4 complex inhibition. [2] This is achieved by activating the protein kinase mammalian target of rapamycin (mTOR). [2]

The effect of Leucine on mTOR is met with the release of insulin. [2] Insulin and leucine together allow skeletal muscle to perform protein synthesis with regards to dietary intake and physiological state. [2]


There is a possible advantage to supplementing with BCAAs for reducing recover time and reaction time during competition for athletes.

BCAAs After Exercise

A common practice in the bodybuilding industry is the ingestion of BCAAs or a fast-acting protein supplement with a simple sugar such as dextrose or fructose immediately after exercise. This explains the relationship between leucine and insulin release and its role in muscle protein synthesis.

A study by Wiśnik, Chmura, Wojciech Ziemba, Mikulski, and Nazar was performed on a sport which requires interval changes or rapid bursts of all-out effort. Soccer, football, bodybuilding, powerlifting, basketball, baseball, and many other contact sports have similar paces of play and bursts.

Players were given a placebo or BCAA complex and were subject to two 45 minute interval workouts between walking and running. After each workout, the subjects took a multiple choice test for 15 minutes then did an active recovery for 20 minutes. Their multiple-choice reaction time (MRT) was calculated after each workout and recovery time. The MRT for the placebo treatment was slightly higher than the BCAA treatment (10%) before and after exercise.

It was concluded that there was no significant difference in supplementing with BCAAs or none at all with regards to mental reaction time or stamina. However the 10% difference may infer that there is a possible advantage to supplementing with BCAAs for reducing recover time and reaction time during competition for athletes. [5]

BCAAs and Muscle Soreness – DOMS

Pull UpsAnother test was performed and documented by Shimomura, Yamamoto, Bajotto, Sato, Murakami, Shimomura, Kobayashi, and Mawatari. It consisted of a squat exercise test on human subjects and recorded the effect of delayed-onset muscle soreness (DOMS). DOMS is essentially the soreness in the muscles days after exercising.

The study showed that BCAA supplementation before exercise reduced the effect of DOMS and accelerated recovery time in the days following the test. [4] These studies show that BCAAs have an obvious place in muscle protein synthesis and recovery, but are not shown to have a significant effect in recovery time reduction or reduction of muscle soreness after exercise. Seeing any extraordinary performance enhancing results from BCAA supplementation is unlikely.

With this research, it can be stated that BCAAs are critical in muscle protein synthesis but are not necessarily beneficial in increasing the rate of synthesis or decreasing the duration of muscle protein synthesis. They must be ingested throughout the day, or prior to exercising and as soon as possible after exercising to achieve optimal results.

Finding Dietary Sources of BCAAs

Where in the diet are BCAAs? Good sources of complete proteins (proteins which contain all the essential amino acids) include animal proteins (meat and dairy), whey and casein supplements, eggs, and plant foods such as soy products.

Typically, in the modern bodybuilding industry protein supplements and powders are loaded up with BCAAs. With so many sources of BCAAs, which is the optimum source for optimal recovery?

A study was done by Reidy et al, which studied the ingestion of protein blends or single protein sources in supplement or powdered form after resistance training. [3] There are many different forms of protein from hydrolyzed isolates to concentrated whey protein. The study hypothesized that a blend of dairy proteins and soy protein would have the optimal delivery of amino acids and BCAAs and promote faster fractional synthetic rate (FSR). [3]

19 adults were studied before and after ingesting a relatively equal amount of either a protein blend, or whey protein supplement. [2] The results showed that initially, each supplement provided a similar rise in FSR. FSR began to drop in the late period for the whey protein group, but stayed elevated for the protein blend group.

Protein blend ingestion after exercise shows a capability of prolonging blood aminoacidemia, mTOR signaling, and skeletal muscle protein synthesis. With this being said a blend of dairy and soy proteins, immediately following a workout can be an effective nutritional supplement. [3]

BCAAs, Exercise and Muscle Protein Synthesis

BCAAs play a critical role in skeletal muscle protein synthesis following breakdown during exercise. BCAAs, primarily leucine, are the key amino acids involved in skeletal muscle tissue synthesis.

Studies have shown supplementing with BCAAs before and after exercise to be somewhat effective in reducing recovery time, increasing synthetic rate, and reducing post-exercise muscle soreness. Though the diet can give an adequate amount of BCAAs, supplementing can be effective before and after exercise because they are absorbed faster. Supplements containing BCAAs are often powders or capsules which can be immediately absorbed in the body.

A study has shown that a blend of dairy proteins (whey and casein) and soy protein can be an effective supplement to give the muscles optimal synthetic rate and sustainability. Many athletes swear by BCAA complexes to fuel their recovery and give them the extra edge. The fact of the matter is that even though the supplements can be absorbed faster and that studies have shown protein blends to keep synthetic rates elevated, there is really no significant correlation the BCAA supplementation and an increase in performance over the rest of the pack.

Being conscious about what goes in the body, especially around periods of intense training is critical to an increase in performance, but research does not firmly support the use of BCAAs as an essential ergogenic aid. Focusing on a well-balanced diet, consisting of whole grains, fruits and vegetables, lean proteins, and healthy fats will give the athlete all they need in regards to nutritional backing to their training and recovery.


1) Hao C, Saksa K, Feiyi Z, Qiu J, Liming X. Genetic analysis of pathway regulation for enhancing branched-chain amino acid biosynthesis in plants. Plant Journal. 2010, August;63(4);573-583.
2) Norton LE, Layman DK. Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise. Journal Nutrition. 2006 February;136(2);533S-537S.
3) Reidy P, Walker DK, Dickinson JM, Gundermann DM, Drummond MJ, Timmerman KL, Fry CS, Borack MS, Cope MB, Mukherjia, R, et al. Protein blend ingestion following resistance exercise promotes human muscle protein synthesis. Journal Nutrition. 2013 April;143(4);410-416.
4) Shimomura Y, Yamamoto Y, Bajotto G, Sato J, Murakami T, Shimomura N, Kobayashi H, Mawatari K. Nutraceutical effects of branched-chain amino acids on skeletal muscle. Journal Nutrition. 2006 February;136(2);529S-532S.
5) Wisnik P, Chmura J, Wojciech Ziemba A, Nazar K. The effect of branched chain amino acids on psychomotor performance during treadmill exercise of changing intensity simulating a soccer game. Applied Physiology, Nutrition, and Metabolism. 2011 December;36(6);856-862.

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Name: Dalton Campbell

Bio: I am an ACSM Certified Personal Trainer, with a BS in Biology and Nutrition and Wellness from Bridgewater College in beautiful Bridgewater, Virginia. I have been an athlete since I was a kid, playing six sports in high school!