Effect of carbohydrate ingestion on glycogen resynthesis in human liver and skeletal muscle, measured by C-13 MRS

This study investigated the effect of carbohydrate (CHO) ingestion on poste xercise glycogen resynthesis, measured simultaneously in liver and muscle ( n = 6) by C-13 magnetic resonance spectroscopy, and subsequent exercise cap acity (n = 10). Subjects cycled at 70% maximal oxygen uptake for 83 +/- 8 m in on six separate occasions. At the end of exercise, subjects ingested 1 g /kg body mass (BM) glucose, sucrose, or placebo (control). Resynthesis of g lycogen over a 4-h period after treatment ingestion was measured on the fir st three occasions, and subsequent exercise capacity was measured on occasi ons four through six. No glycogen was resynthesized during the control tria l. Liver glycogen resynthesis was evident after glucose (13 +/- 8 g) and su crose (25 +/- 5 g) ingestion, both of which were different from control (P < 0.01). No significant differences in muscle glycogen resynthesis were fou nd among trials. A relationship between the CHO load (g) and change in live r glycogen content (g) was evident after 30, 90, 150, and 210 min of recove ry (r = 0.59-0.79, P < 0.05). Furthermore, a modest relationship existed be tween change in liver glycogen content (g) and subsequent exercise capacity (r = 0.53, P < 0.05). However, no significant difference in mean exercise time was found (control: 35 +/- 5, glucose: 40 +/- 5, and sucrose: 46 +/- 6 min). Therefore, 1 g/kg BM glucose or sucrose is sufficient to initiate po stexercise liver glycogen resynthesis, which contributes to subsequent exer cise capacity, but not muscle glycogen resynthesis.