BACKGROUND: Impaired glucose tolerance (IGT) elevates type 2 diabetes and cardiovascular disease (CVD) risk above and beyond impaired fasting glucose (IFG) alone. Endothelial dysfunction and arterial stiffness have been implicated in chronic disease and linked to reduced aerobic fitness. However, it is unknown if the presence of IGT attenuates vascular function in people with IFG. We tested the hypothesis that adults with IFG+IGT have endothelial dysfunction and arterial stiffness in relation to low aerobic fitness when compared with IFG counterparts. METHODS: Middle-aged, obese adults with IFG (n=11, 58.3±10yrs; 34.0±7.4 kg/m2; (FBG: 105.6±6.1mg/dl, 2-hr glc: 120.7±28.1mg/dl) and IFG+IGT (n=14, 61±8.1yrs; 33.1±3.3 kg/m2; FBG: 104.2±10.5mg/dl, 2 hour glc: 165.4±2mg/dl) were compared in this cross-sectional study following a 75g OGTT screening based on ADA criteria. Aerobic fitness (VO2peak) was assessed with a cycle ergometer via indirect calorimetry, and body fat was determined by BIA (InBody®). After an overnight fast, brachial artery flow mediated dilation (FMD) was used to assess endothelial function by ultrasound and arterial stiffness was determined via augmentation index (AI) and pulse wave velocity (PWV) via applanation tomography. A 180-min OGTT was also performed to assess glucose tolerance. RESULTS: Although there was no significant difference between IFG and IFG+IGT for body fat (P=0.94), VO2peak (P=0.46), FMD (P=0.42), AI (P=0.71), or PWV (P=0.95), elevated VO2peak was strongly correlated with a higher FMD in people with IFG+IGT (r=0.57, P=0.04), but not IFG (r=0.1, P=0.99). Moreover, elevated postprandial blood glucose at 180 min was associated with lower VO2peak (r=-0.51, P=0.06) and FMD (r=-0.54, P=0.05) in IFG+IGT, but not IFG (r=-0.19, P=0.57; r=-0.22, P=0.52, respectively). CONCLUSION: Endothelial function was significantly related to aerobic fitness in adults with IFG+IGT but not IFG. These data highlight that post-prandial hyperglycemia may modify vascular function and training adaptation uniquely between prediabetes phenotypes. Additional research is needed to determine the effect of training across exercise doses on skeletal muscle vascular glucose regulation to optimize diabetes and/or CVD prevention.