The effects of an amino acid mixture beverage on glucose tolerance, glycogen replenishment, muscle damage, and anaerobic exercise performance
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Recent research suggests that amino acids, such as leucine and isoleucine, can improve glucose tolerance in vivo and in vitro animal models by accelerating glucose uptake in peripheral tissues and stimulate glycogen synthesis in vitro in the absence of insulin. Our laboratory recently found that gavaging normal Sprague-Dawley rats with an amino acid mixture, composed of isoleucine, leucine, cystine, methionine, and valine, improved blood glucose response during an oral glucose challenge without an increase in the plasma insulin response. The blood glucose-lowering effect of the amino acid mixture was due to an increase in skeletal muscle glucose uptake. These results suggest that this amino acid supplement acutely improves muscle insulin sensitivity and blood glucose homeostasis. However, the effect of this amino acid mixture on glucose tolerance and muscle glycogen synthesis in humans has not been investigated. Some studies have also shown that daily supplementation or acute ingestion of amino acids may prevent muscle damage that occurs as a result of a prolonged, intense endurance exercise or strength training and therefore improves force production and exercise performance. However, the effects of the addition of an amino acid mixture to carbohydrate supplement on muscle damage after a prolonged endurance exercise, as well as on the subsequent anaerobic exercise performance, have not been characterized. Therefore, in this series of two studies, the effects of an amino acid mixture, composed of isoleucine, leucine, cyctine, methionine, and valine, on glucose tolerance, muscle glycogen resynthesis, muscle damage, and anaerobic exercise performance were investigated. Study 1 demonstrated that our amino acid mixture lowered the glucose response to an OGTT in healthy overweight/obese subjects in an insulin-independent manner. Study 2 demonstrated that both high and low dosages of amino acid mixture were effective in lowering blood glucose response to a carbohydrate bolus in athletes postexercise. High dosage of amino acid mixture was more potent in glucose regulation by providing a higher insulin response and amino acid effect. However, our amino acid mixture had no effects on post exercise muscle glycogen synthesis, exercise-induced muscle damage or subsequent anaerobic performance. Taken together, the results of this research series suggest that an amino acid mixture, composed of isoleucine and 4 additional amino acids, attenuates the glucose response to a glucose bolus in an insulin-independent manner, but does not enhance muscle glycogen restoration following exercise or prevent exercise-induced muscle damage.