Abstract
We investigated the effects of nutrient intake timing on glycogen accumulation and its related signals in skeletal muscle after an exercise that did not induce large glycogen depletion. Male ICR mice ran on a treadmill at 25 m/min for 60 min under a fed condition. Mice were orally administered a solution containing 1.2 mg/g carbohydrate and 0.4 mg/g protein or water either immediately (early nutrient, EN) or 180 min (late nutrient, LN) after the exercise. Tissues were harvested at 30 min after the oral administration. No significant difference in blood glucose or plasma insulin concentrations was found between the EN and LN groups. The plantaris muscle glycogen concentration was significantly (p < 0.05) higher in the EN group—but not in the LN group—compared to the respective time-matched control group. Akt Ser473 phosphorylation was significantly higher in the EN group than in the time-matched control group (p < 0.01), while LN had no effect. Positive main effects of time were found for the phosphorylations in Akt substrate of 160 kDa (AS160) Thr642 (p < 0.05), 5′-AMP-activated protein kinase (AMPK) Thr172 (p < 0.01), and acetyl-CoA carboxylase Ser79 (p < 0.01); however, no effect of nutrient intake was found for these. We showed that delayed nutrient intake could not increase muscle glycogen after endurance exercise which did not induce large glycogen depletion. The results also suggest that post-exercise muscle glycogen accumulation after nutrient intake might be partly influenced by Akt activation. Meanwhile, increased AS160 and AMPK activation by post-exercise fasting might not lead to glycogen accumulation.
Highlights
Glycogen stored in skeletal muscle is the predominant energy source for muscle contraction when the exercise intensity is moderate to high in humans [1,2,3]
While previous studies revealing a relationship between nutrient intake timing and post-exercise glycogen recovery have used severe exercise protocols to deplete glycogen storage [8,9,10], in the present study we used moderate endurance exercise without prolonged fast
Nutrient intake immediately after an endurance exercise in the fed state significantly increased plantaris muscle glycogen concentration, while nutrient intake at 180 min after exercise appeared to have no effect on skeletal muscle glycogen accumulation in mice
Summary
Glycogen stored in skeletal muscle is the predominant energy source for muscle contraction when the exercise intensity is moderate to high in humans [1,2,3]. The glycogen level in skeletal muscle is considered as a major determinant of exercise performance. Skeletal muscle glycogen repletion should be a primary goal in the preparation for subsequent training/competitive games. In many sport nutrition guidelines, carbohydrate and protein intake is recommended as the most effective means of post-exercise glycogen accumulation, because these nutrients increase the availability of glucose, a primary source of glycogen synthesis, and stimulate the secretion of insulin, a hormone-activating glucose uptake and glycogen synthesis [5,6,7].
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