A: basal insulin secretion rate over basal glucose concentration [basal sensitivity index (Φb)] in normal glucose tolerance (NGT), impaired fasting glucose (IFG), and IFG/impaired glucose tolerance (IGT) during the glucose step-up procedure. Values are means ± SE. B: the stimulatory effect of the rate of change in glucose on insulin secretion [dynamic β-cell responsivity index (Φd)] in NGT, IFG, and IFG/IGT during the glucose step-up procedure. Values are means ± SE. *P = 0.05 vs. NGT. C: the stimulatory effect of glucose on insulin secretion at a steady-state level above basal [static responsivity index (Φs)] in NGT, IFG, and IFG/IGT during the glucose step-up procedure. Values are means ± SE. P = 0.07, NGT vs. IFG/IGT. D: the global effect of glucose on insulin secretion [global β-cell response to glucose (Φg) = Φs × Φd] in NGT, IFG, and IFG/IGT during the glucose step-up procedure. Values are means ± SE. P = 0.07, NGT vs. IFG/IGT.