Objective: Depletion of glycogen stores is associated with fatigue during both sprint and endurance exercises and therefore it is considered important to maintain adequate tissue stores of glycogen during exercise. The aims of the present study in rats were therefore to investigate the effects of preexercise supplementation with carbohydrate and whey protein hydrolysates (WPH) on glycogen content, and phosphorylated signaling molecules of key enzymes that regulate glucose uptake and glycogen synthesis during exercise. Methods: Male SD rats were used in the study (n = 7/group). Prior to exercise, one group of rats was sacrificed, whereas the other groups were given either water, glucose, or glucose plus WPH solutions. After ingestion of the test solutions, glycogen-depleting exercise was carried out for 60 min. The rats were then sacrificed and the triceps muscles excised quickly. Results: Compared to water or glucose only, preexercise ingestion of glucose plus WPH caused a significant attenuation of muscle glycogen depletion during the postexercise period. Coingestion of glucose and WPH also significantly lowered phosphorylated glycogen synthase levels compared to ingestion of water only. In the glucose plus WPH group, the levels of phosphorylated Akt were increased significantly compared to the group ingesting water only, while the levels of phosphorylated PKC were significantly higher than in the groups ingesting only water or glucose. Conclusion: Taken together, these results indicate that, compared to ingestion of glucose or water only, preexercise ingestion of carbohydrate plus WPH activates skeletal muscle proteins of key enzymes that regulate glucose uptake and glycogen synthesis during exercise, thereby attenuating exercise-induced glycogen depletion.
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