Resumen de Impact of Caffeine and Protein on Postexercise Muscle Glycogen Synthesis

Milou Beelen, Janneau Van Kranenburg, Joan M. Senden, Harm Kuipers, Luc J.C. van Loon

• Background: Both protein and caffeine coingestion with CHO have been suggested to represent effective dietary strategies to further accelerate postexercise muscle glycogen synthesis in athletes.

  Purpose: This study aimed to assess the effect of protein or caffeine coingestion on postexercise muscle glycogen synthesis rates when optimal amounts of CHO are ingested.

  Methods: Fourteen male cyclists were studied on three different test days. Each test day started with a glycogen-depleting exercise session. This was followed by a 6-h recovery period, during which subjects received 1.2 g·kg-1·h-1 CHO, the same amount of CHO with 0.3 g·kg-1·h-1 of a protein plus leucine mixture (CHO + PRO), or 1.7 mg·kg-1·h-1 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 6 h of postexercise recovery.

  Results: The plasma insulin response was higher in CHO + PRO compared with CHO and CHO + CAF (P < 0.01). Plasma glucose responses and glucose appearance rates did not differ between experiments. Muscle glycogen synthesis rates averaged 31 ± 4, 34 ± 4, and 31 ± 4 mmol·kg-1 dry weight·h-1 in CHO, CHO + PRO, and CHO + CAF, respectively (P = NS). In accordance, histochemical analyses did not show any differences between net changes in Type I and Type II muscle fiber glycogen content between experiments.

  Conclusions: Coingestion of protein or caffeine does not further accelerate postexercise muscle glycogen synthesis when ample amounts of CHO (1.2 g·kg-1·h-1) are ingested