L-Valine is an amino acid which aids in muscular development and in the regular maintenance of the nervous system. It is one of three Branch Chain Amino Acids (BCAAs), the other two being Isoleucine and Leucine.
About 1/4 of overall protein intake in a standard diet is in the form of BCAAs, and the body uses them to support healing of damaged skin and muscles (among other things). L-Valine is considered an essential amino acid because the body cannot provide significant enough amounts on its own. It must be found through supplementation or other dietary means.
In order for muscles to metabolize correctly, L-Valine lowers the speed of muscle breakdown during exercise and increases the rate of glucose production. Valine is also important for tissue repair and is primarily responsible for maintaining nitrogen levels and for acting as a direct energy source for muscles. After intense exercise, levels of Valine are usually lowered significantly. Therefore, it is best to take Valine one hour before exercise to help balance out what is subsequently lost. This quickens the pace of muscle recovery.