During long-term and sustained exercise, muscles use large amounts of amino acids as a source for energy. The body prefers to use BCAAs for energy, since they readily replace glucose in the energy production pathways. As muscles begin to use BCAAs, the amounts of these amino acids drop, which allows tryptophan to enter the brain, inducing fatigue and tiredness. Research shows that supplementation with branched-chain amino acids can prevent central fatigue by tightly regulating the amount of tryptophan. Supplementation before and during exercise has been shown to help enhance performance. Branched-chain amino acids include leucine, isoleucine and valine. These amino acids are needed for the maintenance of muscle tissue during physical stress and intense exercise. From the perspective of athletes, BCAAs function as anabolic agents and induce sparing, which allows the body to burn fat and not muscle. Nutrient needs often increase faster than calorie needs in athletes. Ultimate Nutrition is committed to providing athletes with the best products to fulfill exactly those needs. Ultimate Nutrition's 100% Crystalline BCAA 12,000 Powder is one product designed to increase endurance, lengthen the time to fatigue and improve performance.