BCAA's have become a popular supplement in recent years and for very good reason. BCAA's are made up of the essential amino acids Leucine, Isoleucine, and Valine and are usually sold in a 2:1:1 ratio. BCAA's can be used as fuel for the production of energy or to construct new proteins. As they are essentially calorie-free gram for gram, BCAA's make a perfect pre-cardio supplement that can help prevent the breakdown of muscle during aerobic activity. Studies have been conducted that show supplemental BCAA's can spare muscle during intense endurance exercise such as that involved in long duration cardio. This does not mean you should indulge in excessively long cardio sessions in your attempts to burn fat, but it does indicate that by using BCAA's you can potentially spare precious muscle tissue from being used as energy.