To test the hypothesis that physical inactivity impairs the exercise-induced modulation of pyruvate dehydrogenase (PDH), 6 healthy normally physically active male subjects completed 7 days of bed rest. Before and immediately after the bed rest, the subjects completed an OGTT and a one-legged knee extensor exercise bout (45min at 60% Wmax) with muscle biopsies obtained from vastus lateralis before, immediately after exercise, and at 3h of recovery. Blood samples were taken from the femoral vein and artery before and after 40min of exercise. Glucose intake elicited a larger (P=0.05) insulin response after bed rest than before, indicating glucose intolerance. There were no differences in lactate release/uptake across the exercising muscle before and after bed rest, but glucose uptake after 40min of exercise was larger (P=0.05) before bed rest than after. Muscle glycogen content tended to be higher (0.05