Effects of endurance exercise training on muscle glycogen accumulation in humans

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Abstract
The purpose of this investigation was to determine whether endurance exercise training increases the ability of human skeletal muscle to accumulate glycogen after exercise. Subjects (4 women and 2 men, 31 ± 8 yr old) performed high-intensity stationary cycling 3 days/wk and continuous running 3 days/wk for 10 wk. Muscle glycogen concentration was measured after a glycogen-depleting exercise bout before and after endurance training. Muscle glycogen accumulation rate from 15 min to 6 h after exercise was twofold higher ( P < 0.05) in the trained than in the untrained state: 10.5 ± 0.2 and 4.5 ± 1.3 mmol ⋅ kg wet wt−1⋅ h−1, respectively. Muscle glycogen concentration was higher ( P < 0.05) in the trained than in the untrained state at 15 min, 6 h, and 48 h after exercise. Muscle GLUT-4 content after exercise was twofold higher ( P < 0.05) in the trained than in the untrained state (10.7 ± 1.2 and 4.7 ± 0.7 optical density units, respectively) and was correlated with muscle glycogen concentration 6 h after exercise ( r = 0.64, P < 0.05). Total glycogen synthase activity and the percentage of glycogen synthase I were not significantly different before and after training at 15 min, 6 h, and 48 h after exercise. We conclude that endurance exercise training enhances the capacity of human skeletal muscle to accumulate glycogen after glycogen-depleting exercise.