BCAA is a general term for the essential amino acids valine, leucine, and isoleucine that are metabolized and used as sources of muscle enegy. They are referred to as Branched Chain Amino Acids because the molecular structure of these three amino acids includes branches.
They have recently been identified as being very important to muscles since they are found in large quantities in muscle protein.
The chart on the right shows the main effects BCAA may have during exercise.
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Amino acids, including BCAA, are elements of body proteins futhermore; recent research has also confirmed that they each have their own unique physiological effects. For this reason, there is a greater demand for amino acids as supplements during exercise, but as of 2005 there were almost no studies demonstrating increased exercise performance due to amino acid intake. That's why Otsuka Pharmaceutical's Saga Nutraceuticals Research Institute conducted studies on the effect of BCAA on exercise performance and confirmed that it does indeed have an effect on long-distance and strenuous exercises.
This page describes the studies that have been done on BCAA.