Postexercise Muscle Glycogen Synthesis with Combined Glucose and Fructose Ingestion

Abstract

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 gIhj1) or GF (G = 60 gIhj1; F = 30 gIhj1) commencing immediately after exercise and every 30 min thereafter. Results: Immediate postexercise muscle glycogen concentrations were similar in both trials (G = 128 T 25 mmolIkgj1 dry muscle (dm) vs GF = 112 T 16 mmolIkgj1 dm; P 9 0.05). Total glycogen storage during the 4-h recovery period was 176 T 33 and 155 T 31 mmolIkgj1 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 mmolIkgj1 dmIhj1 vs GF = 39 T 8 mmolIkgj1 dmIhj1, 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 È0.8 mmolILj1, P G 0.05). Conclusions: Glucose and glucose/fructose (2:1 ratio) solutions, ingested at a rate of 90 gIhj1, are equally effective at restoring muscle glycogen in exercised muscles during the recovery from exhaustive exercise.