Both micro and macrovascular adaptations contribute to the mechanisms by which reduced physical activity increases the risk for cardiovascular disease and insulin resistance. In a parallel abstract,1 the authors report that 6 weeks of high-intensity interval training (HIT) improves insulin sensitivity. Here the authors aim to investigate whether changes in vascular function play a potential role in this improvement of insulin sensitivity. Eight, young sedentary males (age: 23±2 years, BMI 24.5±1.5 Kg/m2) took part in 6 weeks of HIT involving four to six, 30-s Wingate tests separated by 4.5 min of recovery, performed three times per week. Calf microvascular filtration capacity (Kf) which is an indirect measure of muscle capillary density, was measured using venous occlusion plethysmography. Arterial stiffness was assessed using applanation tonometry (SphygmoCor) to determine peripheral (PPWV) and central pulse wave velocity (CPWV), and augmentation index normalised to 75 beats per minute (AIx at 75 bpm). Blood pressure and insulin sensitivity (oral glucose tolerance test) were also measured pre and post training. Calf microvascular Kf improved after training by 43% (2.81±0.30 ml/min vs 4.02±0.70 ml/min 100 ml/mm Hg×10−3; p<0.05). CPWV and PPWV showed a trend to decrease after training (CPWV 4.8±0.3 m/s vs 4.5±0.3 m/s; p=0.053, PPWV 6.4±0.6 m/s vs 5.9±0.4 m/s; p=0.098). No significant change was observed in AIx at 75 bpm (p=0.114). Resting systolic and diastolic BP decreased after training (systolic 119±2 mm Hg vs 114±2 mm Hg; p<0.05, diastolic 63±3 mm Hg vs 59±2 mm Hg; p<0.05). In the parallel study the authors observe increases in insulin sensitivity. The authors conclude that low volume HIT is an effective method to elicit improvements in both micro and macrovascular function which are likely to be mechanistically related to the observed improvements in insulin sensitivity.