Branched Chain Amino Acids

Of the amino acids discussed, three of them are termed "branched-chain" based on their structure. They are leucine, isoleucine, and valine. They are special because they can be used as an energy source for the muscles when needed. The use of these amino acids may come into play late in endurance exercise when glycogen stores are running low. About 25 percent of the protein in whole food sources is made up of these branched-chain amino acids. Despite their presence in food, supplement enthusiasts have investigated their role as an ergogenic aid.

Several studies have investigated the potential for performance improvements from branched-chain amino acids as a whole. Many have focused on their role in combating fatigue and fighting the effects of overtraining. Branched-chain amino acids present a theoretical advantage because they compete with tryptophan, an amino acid that is associated with mental fatigue (think about your post-Thanksgiving dinner nap; turkey has tryptophan). In theory, if you provide more of these branched chains, it should help to delay this fatigue. Thus far the role they have in fatigue hasn't been conclusive, according to the research.

There may be some relationship between branched chains and immune function, but this needs some work as well.

As a stand-alone branched chain, leucine has been investigated for its role in postexercise muscle synthesis. This research has shown some promising results for an additional benefit from protein with added leucine compared to the typical carbohydrate recovery intake.


As you can imagine, building muscle is no easy task. It is quite a chore, requiring a stimulus and an intricate flow of cellular changes. Muscle growth will not occur if there is not a stimulus (i.e., physical activity or a heavy load, such as in resistance training). After stimulation, a number of events on the cellular level lead to muscle repair and subsequent growth. At the lowest level, muscles will grow when protein synthesis exceeds protein breakdown. Over an extended period of time, when this stimulus is consistently introduced, the muscles will hypertrophy (get bigger) and strength will increase. The extent to which the muscles will grow in size and strength depends on a variety of hormonal factors as well as on gender, age, and body size. At the heart of muscle growth, given a stimulus such as resistance training, you need protein to make the process successful.

The bottom line is that branched chains play a role in energy metabolism and may have some benefit to the athlete. Stay tuned as the research progresses.

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