The branched chain amino acids (BCAA) include leucine, isoleucine, and valine.  They comprise about 18 percent of the total amino acids and 35 percent of the essential amino acids in skeletal muscle.  BCAA's decrease in muscle during intense exercise.  Japanese researchers found that supplying BCAA's before a workout decreased muscle damage and chemical markers of muscle cell damage by approximately 20 percent.  Muscle force measured three days after the workout was 20 percent greater in people who consumed the BCAA supplement.  (International Journal of Sport Nutrition and Exercise Metabolism, 20:  236-244, 2010)