Postexercise Muscle Glycogen Synthesis with Combined Glucose and Fructose Ingestion

WALLIS, G. A., C. J. HULSTON, C. H. MANN, H. P. ROPER, K. D. TIPTON, and A. E. JEUKENDRUP. Postexercise Muscle Glycogen Synthesis with Combined Glucose and Fructose Ingestion. Med. Sci. Sports Exerc., Vol. 40, No. 10, pp. 1789–1794, 2008. Purpose: To evaluate the efficacy of using combined glucose and fructose (GF) ingestion as a means to stimulate short-term (4 h) postexercise muscle glycogen synthesis compared to glucose only (G). Methods: On two separate occasions, six endurance-trained men performed an exhaustive glycogen-depleting exercise bout followed by a 4-h recovery period. Muscle biopsy samples were obtained from the vastus lateralis muscle at 0, 1, and 4 h after exercise. Subjects ingested carbohydrate solutions containing G (90 gIh j1 )o r GF (G = 60 gIh j1 ;F=3 0 gIh j1 ) commencing immediately after exercise and every 30 min thereafter. Results: Immediate postexercise muscle glycogen concentrations were similar in both trials (G = 128 T 25 mmolIkg j1 dry muscle (dm) vs GF = 112 T 16 mmolIkg j1 dm; P 9 0.05). Total glycogen storage during the 4-h recovery period was 176 T 33 and 155 T 31 mmolIkg j1 dm for G and GF, respectively (G vs GF, P 9 0.05). Hence, mean muscle glycogen synthesis rates during the 4-h recovery period did not differ between the two conditions (G = 44 T 8 mmolIkg j1 dmIh j1 vs GF = 39 T 8 mmolIkg j1 dmIh j1 , P 9 0.05). Plasma glucose and serum insulin responses during the recovery period were similar in both conditions, although plasma lactate concentrations were significantly elevated during GF compared to G (by E0.8 mmolIL j1 , P G 0.05). Conclusions: Glucose and glucose/fructose (2:1 ratio) solutions, ingested at a rate of 90 gIh j1 , are equally effective at restoring muscle glycogen in exercised muscles during the recovery from exhaustive exercise.