Beelen, M., Van Kranenburg, J., Senden, J. M., Kuipers, H., & Van Loon, L. J. (2012). Impact of caffeine and protein on post-exercise muscle glycogen synthesis. Medicine & Science in Sports & Exercise, 44, 692-700.

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This study aimed to assess the effect of protein or caffeine co-ingestion on post-exercise muscle glycogen synthesis rates when optimal amounts of carbohydrates are ingested. Male cyclists (N = 14) were studied on three different days. Each day started with a glycogen-depleting exercise session. This was followed by a six-hour recovery, during which Ss received 1.2 g/kg/h CHO, the same amount of CHO with 0.3 g/kg/h of a protein plus leucine mixture (CHO+PRO), or the same amount of CHO with 1.7 mg/kg/h caffeine (CHO+CAF). All drinks were enriched with [U-13C6]-labeled glucose to assess potential differences in the appearance rate of ingested glucose from the gut. Muscle biopsies were collected immediately after cessation of exercise and after six hours of post-exercise recovery.

The plasma insulin response was higher in the CHO+PRO condition compared to CHO-alone and CHO+CAF. Plasma glucose responses and glucose appearance rates did not differ between conditions. Muscle glycogen synthesis rates were similar across conditions. There were no differences between net changes in Type I and Type II muscle fiber glycogen content between conditions.

Implication. Co-ingestion of protein or caffeine does not further accelerate post-exercise muscle glycogen synthesis when ample amounts of CHO (1.2 g/kg/h/) are ingested.

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