Caffeine ingestion does not impede the resynthesis of proglycogen and macroglycogen after prolonged exercise and carbohydrate supplementation in humans.

The purpose of this study was to examine the effects of caffeine (Caf) ingestion on pro- (PG) and macroglycogen (MG) resynthesis in 10 healthy men. Subjects completed two trials, consisting of a glycogen-depleting exercise, while ingesting either Caf or placebo capsules. Throughout recovery, biopsies were taken at 0 (exhaustion), 30, 120, and 300 min, and 75 g of carbohydrate were ingested at 0, 60, 120, 180, and 240 min. Whereas Caf ingestion resulted in a higher blood glucose concentration and decreased glycogen synthase fractional velocity (P <or= 0.05), no effect was observed in either the amount or rate of PG and MG resynthesis. PG concentration increased significantly at each time point during recovery, whereas MG concentration remained unchanged until 120 min. The net rate of PG resynthesis was 115 mmol x kg dw(-1) x h(-1) during the first 30 min of recovery, and then it significantly decreased by 62% throughout the remaining 4.5 h of recovery. The net rate of MG resynthesis was 77% lower than the net rate of PG resynthesis during the first 30 min of recovery and remained constant throughout 5 h of recovery despite increasing levels of insulin. In conclusion, Caf ingestion does not impede the resynthesis of PG or MG after an extensive depletion of muscle glycogen and with the provision of exogenous dietary carbohydrate.