The Impact of Acute Exercise on Vascular Insulin Sensitivity

Purpose: Obesity is associated with decreased sensitivity to insulin, which increases risk of type 2 diabetes and cardiovascular disease. While a single session of exercise increases metabolic insulin sensitivity in adults with obesity, the effect on vascular insulin sensitivity is unknown. Therefore, the primary aim of the current study was to assess the impact of a single bout of exercise on insulin-stimulated responses in conduit arteries and capillaries. A secondary aim included acute exercise implications on insulin-stimulated arterial stiffness as well as metabolic insulin sensitivity. Finally, a tertiary aim was to understand the impact on substrate oxidation. Methods: Eleven sedentary adults (50.0 ± 2.42 yrs; VO2max: 23.5 ± 1.70 ml/kg/min) with central adiposity (waist circumference: 111.8 ± 3.04 cm) completed a control and an acute exercise bout (70% VO2max to expend 400 kcals) condition. After an overnight fast, participants underwent a 2-hr euglycemic-hyperinsulinemic clamp (40 mU·m2·min−1) to determine vascular and metabolic insulin sensitivity. Endothelial function was assessed by brachial artery flow mediated dilation (FMD) while capillary perfusion (microvascular blood volume, MBV), filling rate (microvascular flow velocity, MFV) and blood flow (MBF=MBV*MFV) were assessed using contrast enhanced ultrasound. Systemic aortic waveform was also measured via augmentation index (AIx75) to assess arterial stiffness. Metabolized glucose infusion rate and substrate oxidation was measured to understand metabolic insulin sensitivity and nutrient utilization, respectively. T-tests, repeated measures ANOVAs and correlations were used when appropriate. Significance was accepted as P≤0.05. Results: Exercise did not alter fasting indices of FMD, AIx75, MBV, MFV. However, exercise tended to increase insulin-stimulated MBF (P=0.059) and metabolic insulin sensitivity (P=0.065) compared with control. Further, exercise increased fasting fat oxidation (P=0.03) and insulin-stimulated carbohydrate oxidation (P=0.02) compared with control. Conclusion: A single bout of exercise may improve microvascular blood flow with metabolic insulin sensitivity and fuel selection the following day in adults with central adiposity. Further work is needed to determine vascular responses with different doses of exercise to design optimal lifestyle prescriptions for reducing chronic disease risk.