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High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine

School of Medical Sciences, RMIT University, Bundoora, Victoria, Australia

Submitted 18 October 2007 ; accepted in final form 30 April 2008

We determined the effect of coingestion of caffeine (Caff) with carbohydrate (CHO) on rates of muscle glycogen resynthesis during recovery from exhaustive exercise in seven trained subjects who completed two experimental trials in a randomized, double-blind crossover design. The evening before an experiment subjects performed intermittent exhaustive cycling and then consumed a low-CHO meal. The next morning subjects rode until volitional fatigue. On completion of this ride subjects consumed either CHO [4 g/kg body mass (BM)] or the same amount of CHO + Caff (8 mg/kg BM) during 4 h of passive recovery. Muscle biopsies and blood samples were taken at regular intervals throughout recovery. Muscle glycogen levels were similar at exhaustion [75 mmol/kg dry wt (dw)] and increased by a similar amount (80%) after 1 h of recovery (133 ± 37.8 vs. 149 ± 48 mmol/kg dw for CHO and Caff, respectively). After 4 h of recovery Caff resulted in higher glycogen accumulation (313 ± 69 vs. 234 ± 50 mmol/kg dw, P < 0.001). Accordingly, the overall rate of resynthesis for the 4-h recovery period was 66% higher in Caff compared with CHO (57.7 ± 18.5 vs. 38.0 ± 7.7 mmol·kg dw^–1·h^–1, P < 0.05). After 1 h of recovery plasma Caff levels had increased to 31 ± 11 µM (P < 0.001) and at the end of the recovery reached 77 ± 11 µM (P < 0.001) with Caff. Phosphorylation of CaMK^Thr286 was similar after exercise and after 1 h of recovery, but after 4 h CaMK^Thr286 phosphorylation was higher in Caff than CHO (P < 0.05). Phosphorylation of AMP-activated protein kinase (AMPK)^Thr172 and Akt^Ser473 was similar for both treatments at all time points. We provide the first evidence that in trained subjects coingestion of large amounts of Caff (8 mg/kg BM) with CHO has an additive effect on rates of postexercise muscle glycogen accumulation compared with consumption of CHO alone.

Akt; AMP-activated protein kinase; Ca²⁺/calmodulin-dependent kinase