Two Weeks of Interval vs. Continuous Exercise Training on Endothelial Function in Adults with Prediabetes

Hyperglycemia promotes vascular complications through, in part, an inflammatory-mediated impairment in endothelial function. However, the effects of interval (INT) vs. continuous (CONT) training on endothelial function prior to clinically meaningful weight loss is unknown in adults with prediabetes. Twenty-six subjects with prediabetes (60±1y; 33±1kg/m²; 2h-PG OGTT: 145±7mg/dl) were randomized to 60min of CONT (n=12; 70% of HR_peak) or work-matched INT exercise training (n=14; alternating 3-min at 90 and 50% HR_peak) for 2 weeks. Aerobic fitness (VO₂peak) and body composition (bioelectrical impedance) were assessed before and after training. Flow-mediated dilation (FMD) was measured after an overnight fast during a 2-h 75g OGTT (0, 60 and 120min) to assess endothelial function. Post-prandial FMD stimulation was averaged and defined as the percent change from fasting. Glucose tolerance was calculated by total area under the curve. Fasting plasma VCAM and ICAM were also assessed as indicators of vascular inflammation. Both interventions improved VO₂peak and reduced body fat (P<0.004). Although VCAM (P=0.009) and glucose tolerance (P=0.08) were reduced following both treatments, there was no effect on ICAM or fasting and post-prandial FMD. However, impaired fasting FMD prior to training was correlated with enhanced fasting FMD (r=-0.81, P=0.001) as well as FMD stimulation (r=0.46, P=0.03) post-training. Further, adults with the greatest improvement in fasting FMD after training had the smallest change in post-prandial FMD (r=-0.59, P=0.004). Lowering of VCAM after training was linked to this smaller change in post-prandial FMD (r=0.41, P=0.06) and enhanced fasting FMD (r=-0.38, P=0.05). Taken together, endothelial function is not improved after short-term training, regardless of intensity. However, prediabetic adults with impaired endothelial function at baseline exhibit exercise-induced improvement in FMD, which is linked to vascular inflammation.