Summary Previous studies have shown that the short-term intake of a high-fat diet (HFD) impairs glucose metabolism. In this study, we investigated the influences of pre-exercise HFD intake for 3 d on post-exercise glycogen repletion in skeletal muscle in ICR mice. Mice received either an HFD (57% kcal from fat, 23% kcal from carbohydrate; HFD group) or standard laboratory chow (13% kcal from fat, 60% kcal from carbohydrate; Con group) for 3 d before exercise. Mice performed treadmill running at 25 m/min for 60 min and were orally administered a glucose (2 mg/g body weight) solution immediately after and at 60 min after exercise. A negative main effect of pre-exercise HFD intake was observed for skeletal muscle glycogen concentration from the pre-exercise phase to 120 min of post-exercise recovery (p,0.01). Blood glucose concentration in the HFD group was significantly higher than in the Con group at 120 min after exercise (p,0.01). No significant difference was observed in plasma insulin concentration. There were no significant between-group differences in the phosphorylation state of Akt Thr308, AMPK Thr172, AS160 Thr642, or glycogen synthase Ser641 or in glucose transporter 4 protein levels during post-exercise recovery. Our results suggest that the intake of a pre-exercise HFD for 3 d affects post-exercise glycogen repletion in skeletal muscle without impairing the insulin signaling cascade. Key Words skeletal muscle, post-exercise recovery, high-fat diet, glucoseThe pre-exercise glycogen store in skeletal muscle is considered a major determinant of exercise performance during moderate-to high-intensity exercise (1-4). When exercise intensity exceeds around 60-65% VO2max, the skeletal muscle glycogen store is the predominant source of energy (5, 6). Moreover, recent studies suggest that glycogen per se is important for skeletal muscle force production by the modulating excitationcontraction coupling process (7). When individuals are involved in multiple training sessions and competitions over successive days or within a day, enhancing glycogen repletion in skeletal muscle after exercise is essential for improving performance during subsequent exercise.Some athletes alter their dietary composition of carbohydrate and fat for several days to enhance their exercise performance. For example, adaptation to a ketogenic diet, which severely restricts carbohydrate intake (,20 g/d or 5% of total daily energy intake) and contains high fat levels and an adequate amount of protein, has been shown to be useful for weight control without detrimental effects on skeletal muscle mass, power output, or strength after not only long-term (.2 wk) but also short-term (7 d) administration (8-10). Adaptation to a ketogenic diet increases fat utilization and reduces carbohydrate reliance during exercise without impairing endurance capacity at 62-64% VO 2max under a state of insufficient carbohydrate availability (overnight fasting) (11). However, as a ketogenic diet sometimes causes side effects, including increased perceived exertio...