MUSCLE GLYCOGEN-STORAGE AFTER PROLONGED EXERCISE - EFFECT OF THE GLYCEMIC INDEX OF CARBOHYDRATE FEEDINGS

The effect of the glycemic index (GI) of postexercise carbohydrate int ake on muscle glycogen storage was investigated. Five well-trained cyc lists undertook an exercise trial to deplete muscle glycogen (2 h at 7 5% of maximal O2 uptake followed by four 30-s sprints) on two occasion s, 1 wk apart. For 24 h after each trial, subjects rested and consumed a diet composed exclusively of high-carbohydrate foods, with one tria l providing foods with a high GI (HI GI) and the other providing foods with a low GI (LO GI). Total carbohydrate intake over the 24 h was 10 g/kg of body mass, evenly distributed between meals eaten 0, 4, 8, an d 21 h postexercise. Blood samples were drawn before exercise, immedia tely after exercise, immediately before each meal, and 30, 60, and 90 min postprandially. Muscle biopsies were taken from the vastus lateral is immediately after exercise and after 24 h. When the effects of the immediate postexercise meal were excluded, the totals of the increment al glucose and insulin areas after each meal were greater (P less-than -or-equal-to 0.05) for the HI GI meals than for the LO GI meals. The i ncrease in muscle glycogen content after 24 h of recovery was greater (P = 0.02) with the HI GI diet (106 +/- 11.7 mmol/kg wet wt) than with the LO GI diet (71.5 +/- 6.5 mmol/kg). The results suggest that the m ost rapid increase in muscle glycogen content during the first 24 h of recovery is achieved by consuming foods with a high GI.