MUSCLE GLYCOGEN ACCUMULATION AFTER ENDURANCE EXERCISE IN TRAINED AND UNTRAINED INDIVIDUALS

Muscle glycogen accumulation was determined in six trained cyclists (T rn) and six untrained subjects (UT) at 6 and either 48 or 72 h after 2 h of cycling exercise at similar to 75% peak O-2 uptake ((V) over dot O-2peak), which terminated with five 1-min sprints. Subjects ate 10 g carbohydrate.kg(-1).day(-1) for 48-72 h postexercise. Muscle glycogen accumulation averaged 71 +/- 9 (SE) mmol/kg (Trn) and 31 +/- 9 mmol/k g (UT) during the first 6 h postexercise (P < 0.01) and 79 +/- 22 mmol /kg (Trn) and 60 +/- 9 mmol/kg (UT) between 6 and 48 or 72 h postexerc ise (not significant). Muscle glycogen concentration was 164 +/- 21 mm ol/kg (Trn) and 99 +/- 16 mmol/kg (UT) 48-72 h postexercise (P < 0.05) . Muscle GLUT-4 content immediately postexercise was threefold higher in Trn than in UT (P < 0.05) and correlated with glycogen accumulation rates (r = 0.66, P < 0.05). Glycogen synthase in the active I form wa s 2.5 +/- 0.5, 3.3 +/- 0.5, and 1.0 +/- 0.3 mu mol.g(-1).min(-1) in Tr n at 0, 6, and 48 or 72 h postexercise, respectively; corresponding va lues were 1.2 +/- 0.3, 2.7 +/- 0.5, and 1.6 +/- 0.3 mu mol.g(-1).min(- 1) in UT (P < 0.05 at O h). Plasma insulin and plasma C-peptide area u nder the curve were lower in Trn than in UT over the first 6 h postexe rcise (P < 0.05). Plasma creatine kinase concentrations were 125 +/- 2 5 IU/l (Trn) and 91 +/- 9 IU/l (UT) preexercise and 112 +/- 14 IU/l (T rn) and 144 +/- 22 IU/l (UT; P < 0.05 vs. preexercise) at 48-72 h post exercise (normal: 30-200 IU/I). We conclude that endurance exercise tr aining results in an increased ability to accumulate muscle glycogen a fter exercise.