Impact of Short-Term Continuous and Interval Exercise Training on Endothelial Function and Glucose Metabolism in Prediabetes

Introduction. The impact of interval (INT) vs. continuous (CONT) exercise training on endothelial function in relation to glucose metabolism prior to clinically meaningful weight loss is unknown in adults with prediabetes. Methods. Twenty-six subjects with prediabetes (60±1 y; 33±1 kg/m²; 2-hr-PG OGTT: 145±7 mg/dl) were randomized to 60 min 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 (VO_2peak) and body composition (bioelectrical impedance) were assessed before and after training. Flow-mediated dilation (FMD) was measured during a 2 h 75 g OGTT (0, 60, and 120 min) to assess endothelial function. Postprandial FMD was calculated as incremental area under the curve (iAUC). Glucose tolerance and insulin were also calculated by iAUC. Fasting plasma VCAM, ICAM, and hs-CRP were also assessed as indicators of vascular/systemic inflammation. Results. Both interventions increased VO_2peak (P=0.002) but had no effect on body fat (P=0.20). Although both treatments improved glucose tolerance (P=0.06) and insulin iAUC (P=0.02), VCAM increased (P=0.01). There was no effect of either treatment on ICAM, hs-CRP, or fasting as well as postprandial FMD. However, 57% of people improved fasting and iAUC FMD following CONT compared with only 42% after INT exercise (each: P=0.04). Elevated VCAM was linked to blunted fasting FMD after training (r=-0.38, P=0.05). But, there was no correlation between fasting FMD or postprandial FMD with glucose tolerance (r=0.17, P=0.39 and r=0.02, P=0.90, respectively) or insulin iAUC following training (r=0.34, P=0.08 and r=0.04, P=0.83, respectively). Conclusion. Endothelial function is not improved consistently after short-term training, despite improvements in glucose and insulin responses to the OGTT in obese adults with prediabetes.