Exercise training and glucose uptake by skeletal muscle in rats.

Glucose uptake rates at various insulin concentrations were compared in perfused hindlimbs of sedentary and endurance exercise-trained (treadmill-running) rats. Rates of glucose uptake by hindlimb muscles were approximately 50% higher in the trained than in the untrained animals on the day after the trained rats' last training session. However, by the 2nd day after the trained rats' last training session (40-46 h without exercise), there were no significant differences in glucose uptake rates between the trained and the sedentary rats' hindlimb muscles either in the absence of insulin, at physiological insulin levels, or at a maximally effective insulin concentration. A bout of exercise, consisting of swimming to fatigue on the day before study, and muscle contraction induced by electrical stimulation, both resulted in significant increases in glucose uptake by the rats' perfused hindlimbs; the magnitude of these increases were similar in the trained and untrained rats. We conclude that differences in muscle glucose uptake between trained and untrained rats are due to residual effects of the last exercise session and that training does not result in a long-term adaptive increase in sensitivity of muscle to insulin.