Effect of different post-exercise sugar diets on the rate of muscle glycogen synthesis

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Abstract
The effect of repeated ingestions of fructose, sucrose, and various amounts of glucose on muscle glycogen synthesis during the first 6 h after exhaustive bicycle exercise was studied. Muscle biopsies for glycogen determination were taken before and after exercise, and every second hour during recovery. Blood samples for plasma glucose and insulin determination were taken before and after exercise, and every hour during recovery. When 0.35 (low glucose: N = 5), 0.70 (medium glucose: N = 5), or 1.40 (high glucose: N = 5) g .cntdot. kg-1 body weight of glucose were given orally at 0, 2, and 4 h after exercise, the rates of glycogen synthesis were (mean .+-. SE) 2.1 .+-. 0.5, 5.8 .+-. 1.0, and 5.7 .+-. 0.9 mmol .cntdot. kg-1 .cntdot. h-1, respectively. When 0.70 g .cntdot. kg-1 body weight of sucrose (medium sucrose: N = 5), or frustose (medium fructose: N = 7) was ingested accordingly, the rates were 6.2 .+-. 0.5 and 3.2 .+-. 0.7 mmol .cntdot. kg-1 .cntdot. h-1. Average plasma glucose levels during recovery were similar in low glucose, medium glucose, and high glucose groups (5.76 .+-. 0.24, 6.31 .+-. 0.64, and 6.52 .+-. 0.24 mM), while average plasma insulin levels were high with higher glucose intake (16 .+-. 1, 21 .+-. 3, and 38 .+-. 4 .mu.U .cntdot. ml-1). The results suggest that: (i) the rate of post-exercise muscle glycogen synthesis increases with increasing oral glucose intake, up to a maximum rate of approximately 6 mmol .cntdot. kg-1 .cntdot. h-1: (ii) fructose ingestion produces a slower rate of glycogen resynthesis than glucose and sucrose ingestion; and (iii) the plasma insulin level does not correlate with the rate of post-exercise muscle glycogen synthesis (r = 0.41, P = 0.25).

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