High dietary carbohydrate (CHO) intake and reduced exercise training are recommended to optimize muscle glycogen stores pre-endurance sports competition. However, the optimal CHO intake to support muscle glycogen synthesis and the dose-response of this relationship are still unknown in athletes who continue training pre-competition. This study investigated the effects of different CHO intakes on muscle glycogen concentration. In a counterbalanced repeated measures design, 11 endurance-trained participants (3 females, 8 males; age, 24 ± 5 years; body mass, 71.2 ± 12.0 kg; V?O2max, 56 ± 6 mL kg-1 min-1) undertook 3 × 5 days of exercise and dietary control. During the final 48 h, participants ingested 6, 8 or 10 g kg-1 day-1 CHO prior to the assessment of muscle glycogen, gastrointestinal (GI) comfort and body composition. Muscle glycogen concentration was significantly higher following 10 vs. 6 and 8 g kg-1 day-1 (635.5 ± 78.0 vs. 460.9 ± 100.7 and 506.1 ± 124.0 mmol kg-1 dry mass, respectively, p < 0.03), with no difference between 6 and 8 g kg-1 day-1 (p = 1.00). There was a strong positive correlation between relative CHO intake (r = 0.71, p < 0.001) and skeletal muscle glycogen concentration. There was no effect of CHO intake on body mass (p = 0.70) or GI symptoms (p > 0.05), except fullness. In conclusion, there was a linear dose-response between dietary CHO intake and muscle glycogen in a protocol mimicking real-world training and nutrition practices, as 10 g kg-1 day-1 achieved the highest muscle glycogen concentrations, with no detectable effect on body mass or GI symptoms, except increased fullness.
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