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Effects of BCAA supplementation on Exercise
BCAAs have an insullin-like effect on glucose, causing a reduction in glucose levels. BCAAs that are ingested before exercise can be oxidized by skeletal muscle and used as energy during the exercise, reducing the need for the liver to increase levels of glycogenolysis. During anaerobic exercise the pyruvate molecules that result from glucose metabolism are converted to lactic acid, the buildup of which can lead to metabolic acidosis with pH levels as low as 6.4. High levels of lactic acid cause glucose metabolism to stop in order to reduce further reduction of pH. BCAA supplementation has been shown to decrease levels of lactic acid the muscle, allowing glucose metabolism to continue. This results in reduced rates of glycogenolysis in the liver and consequently lower plasma levels of glucose. However, studies done regarding long term effects of BCAAs on glucose levels have shown that consistent supplementation of BCAAs do not have a notable effect on blood glucose levels outside of exercise.

Recent studies have also shown that BCAAs reduce the levels of circulating free fatty-acids (FFA) in the blood. FFAs complete for binding sites on albumin with tryptophan, and when levels of FFAs in the blood are decreased, levels of free tryptophan also decreased as more is bound by albumin. During exercise, levels of free tryptophan entering the brain are increased, causing an increase in 5-hydroxytryptamine (5-HT), a contributor to the sensation of fatigue. Through their reduction in levels of FFAs in the blood, BCAAs can help to reduce the levels of free tryptophan entering the brain, and help to reduce the sensation of fatigue as a result of exertion.

BCAAs are also found to reduce the increase in serum levels of ammonia that occurs during exercise. This is done by increasing the amount of ammonia used in glutamine synthesis, preventing an over-accumulation of ammonia in the blood. Increased levels of ammonia in the brain result in lower levels of GABA and Glutamate, causing an increase in central fatigue. Increased levels of ammonia in the muscle tissue also increase phospofructokinase activity (PFK), leading to an increase in lactic acid, a major contributor to muscle fatigue.

In addition, BCAA supplementation has been shown to decrease levels of creatine kinase in muscle cells post exercise. Creatine kinase is an indicator of muscle damage, and is responsible for transferring a phosphate group from ATP to create a creatine phosphate molecule. BCAA supplementation has been shown to decrease levels of creatine kinase, leading to higher levels of intracellular ATP and a lessened sense of fatigue. See also DOMS.