A single bout of prolonged exercise followed by intake of carbohydrate can increase muscle glycogen content far above basal levels. The molecular mechanisms leading to this glycogen supercompensation are still incompletely understood. To investigate this, nine healthy male subjects were studied 3 times during 5 days following knee-extensor exercise of one leg while the other leg served as resting control. Insulin action was evaluated in both legs by euglycemic hyperinsulinemic clamps and leg catherization on day 1 (4 h post exercise), day 2 and day 5 (28 and 100 h post exercise, respectively) while the subjects consumed a eucaloric carbohydrate rich diet (80% CHO) between clamps. In the prior exercised leg, glycogen content was decreased (~65%, day 1, p<0.001), normalized (day 2, p=0.24) and supercompensated (+ ~30%, day 5, p<0.001) compared to the rested leg. Insulin stimulated glucose uptake (ISGU) was markedly (+~40%, p<0.001) increased in the exercise leg 4 h after exercise (day 1) compared to the rested leg. Surprisingly, the level of ISGU was maintained high in the exercised leg on day 2 and 5. Exercise resulted in marked dephosphorylation of GS at sites 3a, 3a +3b and 2+2a and activation of muscle glycogen synthase (GS) on day 1 (p<0.001). This enhanced effect of exercise on GS was preserved the subsequent day. Hexokinase II, but not GLUT 4, protein content was increased (~ + 30%, p<0.01) in the prior exercised muscle throughout the supercompensation regime. We hypothesize that the mechanisms leading to muscle supercompensation involve enhanced insulin stimulated glucose uptake mediated by enhanced capacity for glucose-transport, -phosphorylation and glucose storage. The apparent glycogen independent regulation of these events is novel and questions current thoughts on the regulatory role of glycogen in human muscle insulin action.