Figure 2.

Cardiorespiratory fitness is associated with Si_OGTT, GSIS_OGTT, and DI_OGTT. VO_2max was measured during incremental workload and exhaustive aerobic exercise in subjects representative of a heterogeneous population with respect to age, BMI, adiposity, and glucose tolerance status (white circles, NGT; light-gray squares, IGT; and dark-gray triangles, T2D). VO_2max was directly associated with Si_OGTT (y = 0.00117x + 0.0119) (A) but had an inverse curvilinear log-log relationship with early-phase (log₁₀y = −0.39 log₁₀x + 5.18) (B) and late-phase (log₁₀y = −0.42 log₁₀x + 6.07) (C) GSIS_OGTT. Finally, there were direct linear relationships between VO_2max and early-phase (y = 27.8x + 916) (D) and late-phase (y = 200x + 5,966) (E) DI_OGTT, a measure of pancreatic β-cell insulin secretory compensation for changing insulin sensitivity. Solid and dotted lines represent the regression curves and 95% CIs, respectively, and show unadjusted data.