Protein is a key macronutrient in an athlete’s diet. An adequate intake of protein at the right time provides numerous benefits including enhanced recovery and maintaining or increasing muscle mass 1,2. Proteins are comprised of building blocks called “amino acids” that are bound together in long chains known as polypeptides, which make up an individual protein . In recent years, research has begun to focus on the possible benefits of adding specific amino acids to an athlete’s diet 6, of which a subset of amino acids known as branched-chain amino acids (BCAAs) have received particular attention.

This article will:

  • Outline the structure and function of BCAAs
  • Examine the potential ergogenic benefits of ingesting BCAAs in addition to, or as part of quality protein in the diet of power athletes
  • Examine the potential ergogenic benefits of ingesting BCAAs in addition to, or as part of quality protein in the diet of endurance athletes
  • Provide recommendations for the inclusion of BCAAs in an athlete’s diet that will optimize performance and recovery from exercise

What are Branched Chain Amino Acids (BCAAs)?

BCAAs are considered essential amino acids, which means that they are not synthesized within the body itself and must be obtained from food sources. There are three BCAAs: Leucine, Valine and Isoleucine. BCAAs have a unique chemical structure as illustrated.


The amino acids that make up total skeletal muscle protein comprise of approximately one-third of BCAAs 14. During prolonged exercise BCAAs can be oxidized within the mitochondria of skeletal muscles to produce energy. On the other hand, the six other essential amino acids are mainly metabolized within the liver 11. During prolonged exercise, the quantity of BCAAs that are broken down to produce energy increases significantly 12,13. This can lead to reduced levels of BCAAs within the muscle and as a result they may need to be replaced in the diet.

How do BCAAs enhance exercise performance and/or adaptation to exercise?

BCAAs and the Strength/Power Athlete

BCAA supplementation during strength/power training may help improve protein synthesis and minimize protein degradation and thereby lead to greater gains in fat-free mass 10.

The effects of resistance exercise on muscle protein status

It is well established that resistance training leads to increases in muscle strength and hypertrophy. This type of training causes both protein synthesis (muscle building) and protein degradation (muscle breakdown). Muscle adaptation and development is dependent on the net balance between the two of these processes. Strength athletes should focus on maximizing protein synthesis and minimizing protein degradation. Appropriate nutritional strategies, such as adequate caloric and protein intake, can sway the balance in favour of protein synthesis and optimize muscle adaptation 6.

The role of protein in determining muscle protein status

The determining nutritional factors that tip the balance in terms of protein synthesis or breakdown are debated topics in the current literature. In the past researchers identified an overall increase in amino acid availability as a result of protein supplementation before/during exercise as the key process that favours of protein synthesis 4. Other researchers have argued that it is the presence of a group of amino acids (BCAAs) or a specific amino acid (leucine) that causes this effect 4.

How can BCAAs or leucine supplementation increase protein synthesis or decrease protein degradation?

1. Leucine stimulates an insulin response

Certain amino acids, such as leucine, have been shown to directly stimulate an insulin response 7. Research has shown that ingesting a drink that contains simple carbohydrates, whey isolate and leucine greatly increases post-exercise insulin levels. This is supported by high levels of amino acids and leads to increased skeletal muscle hypertrophy and strength 7.

2. Leucine can initiate translation – a key process in protein synthesis

Translation is a key process within the cell results in protein synthesis. However, translation can be inhibited during and immediately after exhaustive resistance training. Appropriate nutritional strategies can combat this effect. Leucine is the only amino acid that is able to initiate the translation process and in effect “switch on” protein synthesis 15,18

Therefore, given the positive effects of BCAAs and leucine on muscle metabolism,

Supplemental BCAAs/leucine may be necessary to optimize their availability during strenuous exercise, and promote adaptation to exercise training.

BCAAs and the Endurance Athlete

Can BCAAs help to delay fatigue during prolonged exercise?

Endurance athletes need to delay fatigue in order to optimize performance. Fatigue during prolonged exercise can be associated with

  • mechanisms that result in failure of the contractile ability within the muscle (peripheral fatigue)
  • mechanisms that result in specific changes to the central nervous system (central fatigue)

BCAA supplementation and in particular leucine supplementation does indeed seem to improve endurance performance. The mechanisms underlying these ergogenic benefits are presently unclear. One theory that is that BCAA ingestion can combat the effects of central fatigue and therefore improve performance. During prolonged exercise the levels of fatty acids in the blood increase as they are mobilized for energy. Fatty acids compete with tryptophan in the blood to bind with albumin. As a result of there being more fatty acids in the blood there is more competition and therefore smaller amount of tryptophan can bind with albumin. Tryptophan that does not bind with albumin is called free tryptophan. As a result of these processes the amount of free tryptophan in the blood increases during prolonged exercise.

Free tryptophan can enter the central nervous system. It can then be converted to serotonin (which plays a role in the onset of sleep) and the increase in seratonergic activity may lead to central fatigue , causing athletes to either stop exercise or decrease the exercise intensity 8. This theory is known as the central fatigue hypothesis.

However, BCAAs compete with free tryptophan for entry into the central nervous system. Researchers theorized that by increasing BCAAs an athlete could improve performance by decreasing the amount of tryptophan entering the central nervous system. However, currently there is little evidence that directly supports this theory, despite the observation that BCAA supplementation can improve exercise performance.

It is possible that the ergogenic benefits may be related to reduced skeletal muscle damage and an increase in skeletal muscle synthesis in response to long term rather than acute supplementation i.e. indirect and direct effects respectively. Endurance athletes need to optimize their ability to recover between training sessions. BCAAs may play a role in optimizing recovery time – allowing athletes to train harder and longer. Over time, this would lead to improvements in performance.

More recent research suggests that BCAA supplementation immediately before and during prolonged exercise may also provide adpative benefits. In one study, BCAA supplementation attenuated muscle damage during prolonged endurance exercise in untrained college-age men when compared with a carbohydrate drink or water 16 . As a result of less muscle damage during exercise an athlete may need less recovery time and can therefore train more frequently. Over time this would lead to improvements in performance.

Furthermore, recent research suggests that supplementing with BCAAs immediately before and during exercise provides higher levels of BCAAs that can be oxidized during exercise 17. Interestingly, lactate is not produced during BCAA oxidation. High lactate levels can induce fatigue. Therefore, BCAA supplementation may be effective at increasing endurance exercise capacity 17.


  • BCAAs play an important role in many metabolic processes.
  • BCAAs undergo oxidation during exercise and are an important workout fuel 5.
  • Studies have demonstrated that BCAAs are the key amino acids that stimulate protein synthesis (muscle building) after intense exercise 3.
  • They may play a key role in enhancing recovery and/or training adaptations.
  • Therefore, BCAAs may have potential benefits for both endurance and strength/power exercise performance 5.



An 80kg power athlete would consume the following drinks.

Endurance athletes could consume 1 during workout drink for every hour of training.

As with all supplemention, it is best to monitor one’s own progress and adapt nutrient intake accordingly. In this way, you will be implementing a nutrition program that is research based and takes into account individual difference.


Should I supplement with all 3 BCAA’s or just Leucine?

Although a lot of research points to the positive effects of Leucine , all three BCAA’s play a key role in promoting muscle protein synthesis and minimizing protein breakdown. Based on current research a BCAA supplement containing all three BCAA’s would be recommended.


  • Phillips SM: Protein requirements and supplementation in strength sports. Nutrition 20:689–695, 2004.
  • Tarnopolsky MA, Atkinson SA, MacDougall JD, Chesley A, Phillips S, Schwarcz HP: Evaluation of protein requirements for trained strength athletes. J Appl Physiol 73:1986–1995, 1992.
  • Garlick P, Amino Acid Infusion increases the sensitivity of muscle protein systhesis in vitro to insulin: Effect of Branched Chain Amino Acids Biochem J 1988 254(2); 579-584
  • Kreider RB et al. Exercise & Sport Nutrition: Principles, Promises, Science & Recommendations, 2009
  • Henderson SA, Black AL, Brooks GA (1985) Leucine turnover and oxidation in trained rats during exercise. Am J Physiol Endocrinol Metab 249:E137–E144
  • Blomstrand, E. Branched-chain amino acids activate key enzymes in protein synthesis after physical exercise. 2006.
  • Manninen, A. Hyperinsulinaemia, hyperaminoacidaemia and post-exercise muscle anabolism: the search for the optimal recovery drink. 2006.
  • Asker Jeukendrup, Michael Gleeson Sport nutrition: an introduction to energy production and performance , 2010
  • Crowe, M. Effects of dietary leucine supplementation on exercise performance. 2006.
  • Kreider RB Effects of protein and amino-acid supplementation on athletic performance Sportscience 3(1),, 1999
  • Shimomura, Y., Murakami, T., Nakai, N., Nagasaki, M. and Harris, R. A. (2004) Exercise Promotes BCAA Catabolism: Effects of BCAA Supplementation on Skeletal Muscle during Exercise. J Nutr. 134, 1583S-1587S.
  • Rennie, M. J. (1996) Influence of exercise on protein and amino acid metabolism. In: Handbook of Physiology, Sect 12: Exercise: Regulation and Integration of Multiple Systems (Rowell, L. B. & Shepherd, J. T., eds), Chapter 22. 995-1035. American Physiological Society, Bethesda, MD.
  • Kobayashi, r. shimomura, Y., Murakami, T., Nakai, N., Otsuka, M., Arakawa, N., Shimizu, K. and Harris, R. A. (1999) Hepatic branched-chain alpha-keto < acid dehydrogenase complex in female rats: activation by exercise and starvation. J Nutr Sci. Vitaminol. 45, 303-309.
  • Mero, A. Leucine Supplementation and Intensive Training. 1999
  • Norton, L. Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise. 2006.
  • 16. Greer BK, Woodard JL, White JP, Arguello EM, Haymes EM. Branched-chain amino acid supplementation and indicators of muscle damage after endurance exercise. Int J Sport Nutr Exerc Metab. 2007 Dec;17(6):595-607.
  • BCAA supplementation may be effective to increase the endurance exercise capacity. Branched-chain amino acid supplementation increases the lactate threshold during an incremental exercise test in trained individuals. J Nutr Sci Vitaminol (Tokyo). 2009 Feb;55(1):52-8.