The effects of carbohydrate and HMB supplementation on glycogen synthesis post-exercise
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Carbohydrate plus additional protein supplementation provided immediately after exercise has been found to increase the rate of muscle glycogen restoration compared to carbohydrate alone. To examine whether leucine, and/or β-hydroxy-β-methylbutyrate (HMB) to carbohydrate plus protein supplementation affects short-term recovery (45 min) of muscle glycogen, we compared plasma glucose and insulin, the muscle glycogen concentration, and the cellular signaling proteins controlling muscle glycogen synthesis 45 min after supplementation. Rats (n=35) underwent high-intensity resistance exercise followed by supplementation with carbohydrate (CHO: 1.2g/kg body weight), carbohydrate with whey protein (CP: 1.2g CHO + 375mg whey protein/kg body weight), carbohydrate with whey protein plus HMB (CPH: 1.2g CHO + 375mg whey protein + 400mg HMB/kg body weight), carbohydrate with whey protein, HMB plus leucine (CPHL: 1.2g CHO + 375mg whey protein + 400mg HMB + 444mg leucine/kg body weight) or exercise only (CON). Blood samples were collected immediately after exercise and 45 min after supplementations. Muscle samples of plantaris were excised immediately and 45 min post-exercise. Plasma glucose was increased by CHO and CPH supplementation and reduced by CPHL at 45 min post-exercise. Plasma insulin was elevated by CP and CPHL treatments compare to CHO. Muscle glycogen concentration was unaffected by all treatments and did not differ from CON. Phosphorylation of Akt/PKB, GSK3α/β, and GS at 45 min of recovery for all supplements was not significant difference from CON. Phosphorylation of mTOR was significantly increased by CPHL and CP supplementation compared to CON, CHO, and CPH. Phosphorylation of AS160 was markedly reduced by CPH supplementation compared to CON. These results suggest that supplementing with carbohydrate plus protein with or without leucine and its metabolite, HMB, to enhance muscle glycogen replenishment following exercise may not provide an advantage during the early phase of recovery (45 min). Furthermore, there is some indication that HMB may elicit insulin resistance, and this needs further evaluation.