Muscle glycogen accumulation after endurance exercise in trained and untrained individuals

Abstract

Hickner, R. C., J. S. Fisher, P. A. Hansen, S. B. Racette, C. M. Mier, M. J. Turner, and J. O. Holloszy. Muscle glycogen accumulation after endurance exercise in trained and untrained individuals. J. Appl. Physiol. 83(3): 897–903, 1997.—Muscle glycogen accumulation was determined in six trained cyclists (Trn) and six untrained subjects (UT) at 6 and either 48 or 72 h after 2 h of cycling exercise at ∼75% peak O2 uptake (V˙o 2 peak), which terminated with five 1-min sprints. Subjects ate 10 g carbohydrate ⋅ kg−1 ⋅ day−1for 48–72 h postexercise. Muscle glycogen accumulation averaged 71 ± 9 (SE) mmol/kg (Trn) and 31 ± 9 mmol/kg (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 postexercise (not significant). Muscle glycogen concentration was 164 ± 21 mmol/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 was 2.5 ± 0.5, 3.3 ± 0.5, and 1.0 ± 0.3 μmol ⋅ g−1 ⋅ min−1in Trn at 0, 6, and 48 or 72 h postexercise, respectively; corresponding values were 1.2 ± 0.3, 2.7 ± 0.5, and 1.6 ± 0.3 μmol ⋅ g−1 ⋅ min−1in UT ( P < 0.05 at 0 h). Plasma insulin and plasma C-peptide area under the curve were lower in Trn than in UT over the first 6 h postexercise ( P < 0.05). Plasma creatine kinase concentrations were 125 ± 25 IU/l (Trn) and 91 ± 9 IU/l (UT) preexercise and 112 ± 14 IU/l (Trn) and 144 ± 22 IU/l (UT; P < 0.05 vs. preexercise) at 48–72 h postexercise (normal: 30–200 IU/l). We conclude that endurance exercise training results in an increased ability to accumulate muscle glycogen after exercise.