exercise has a number of beneficial effects that can play important roles in the prevention and treatment of the insulin resistance that leads to and mediates type 2 diabetes (23). In addition to increased energy expenditure, which helps to prevent and reverse obesity, exercise has short-term effects that enhance insulin action. Exercise acutely increases muscle glucose transport, and this effect is mediated by an increase in the glucose transporter 4 (GLUT4) isoform of the glucose transporter in skeletal muscle (18). As this effect wears off, it is replaced by an increase in insulin sensitivity (19). As a result of these two adaptations, exercise results in increases in both insulin sensitivity and insulin responsiveness. Insulin sensitivity is evaluated in terms of the concentration of insulin required to induce 50% of its maximal effect on glucose transport (25). An increase in insulin sensitivity causes the insulin dose-response curve to shift to the left so that the insulin concentration required to cause 50% of its maximal effect is lower. Insulin responsiveness, in contrast, determines the magnitude of the increase in glucose transport induced by a maximally effective insulin stimulus (25). An increase in insulin responsiveness causes a larger increase in glucose transport in response to a maximal insulin stimulus and a proportional upward shift in the insulin dose-response curve.