Effects of endurance exercise training on muscle glycogen accumulation in humans

Effects of endurance exercise training on muscle glycogen accumulation in h umans. J.Appl. Physiol. 87(1): 222-226, 1999.-The purpose of this investiga tion was to determine whether endurance exercise training increases the abi lity of human skeletal muscle to accumulate glycogen after exercise. Subjec ts (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 glyco gen concentration was measured after a glycogen-depleting exercise bout bef ore 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 tha n 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 exe rcise. Muscle GLUT-4 content after exercise was twofold higher (P < 0.05) i n the trained than in the untrained state (10.7 +/- 1.2 and 4.7 +/- 0.7 opt ical density units, respectively) and was correlated with muscle glycogen c oncentration 6 h after exercise (r = 0.64, P < 0.05). Total glycogen syntha se activity and the percentage of glycogen synthase I were not significantl y different before and after training at 15 min, 6 h, and 48 h after exerci se. We conclude that endurance exercise training enhances the capacity of h uman skeletal muscle to accumulate glycogen after glycogen-depleting exerci se.