The effect of high and low volume of aerobic interval training on endothelial function in healthy men
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Physical inactivity is a major risk factor for cardiovascular diseases. Exercise training has shown to reduce cardiovascular mortality and induce large health benefits. Today we experience a sedentary “epidemic”, and despite all the evidence pointing out to the importance of regular physical activity in preventing chronic diseases and premature death, most adults fail to meet the minimum requirements. Regular physical activity reduces cardiovascular morbidity and mortality by decreasing the risk factors related to cardiovascular disease. The endothelium lines the inner face of all blood vessels and cardiac chambers. The endothelium is made up of endothelial cells, and regulates vascular tone and cellular adhesion, it controls thrombosis and thrombolysis, and cellular proliferation. Regulation of vessel tone and diameter plays an important role in the balance of tissue oxygen supply and metabolic demand. In healthy arteries an increase in blood flow, and indirectly shear stress, will result in a flow-mediated dilatation (FMD). FMD can therefore be used as an index of endothelial function and vascular health. The presence of cardiovascular risk factors may lead to endothelial dysfunction. Endothelial dysfunction is a good predictor of the development of cardiovascular diseases since endothelial dysfunction usually is present before irregularities in arterial wall becomes apparent. The aim of the present study was to determine whether an exercise intervention consisting of a single 4-minute interval (1-AIT) each exercise training session induced similar cardiovascular adaptations as an exercise intervention consisting of four 4-minute intervals (4-AIT). The exercise training period lasted for 10 weeks with 3 sessions per week. Endothelial function and blood pressure were measured, and blood variables were analyzed at the start and in the end of the exercise training period. The intention was to observe the effect of the different exercise training interventions on the function of the endothelium, the blood pressure and the concentration of the different blood variables. Endothelial function was measured as flow-mediated dilatation (FMD) in the brachial artery using high-resolution vascular ultrasound. Blood pressure was measured automatically using a sphygmomanometer, and blood samples were analyzed for glucose, glycosylated hemoglobin type A1c (HbA1c), high density lipoprotein (HDL), low density lipoprotein (LDL), oxidized-LDL, triglycerides, high-sensitivity serum C-reactive protein (CRP), cholesterol, insulin C-peptide and hemoglobin (Hb). The main findings of the present study were that the endothelial function was unchanged after the exercise training period in both groups (FMD (%) 1-AIT: p=0.97, 4-AIT: p=0.31), with a significant difference between the groups (FMD (%) p=0.013). Mean arterial pressure decreased significant in the 4-AIT group with 4.7% (p=0.007) compared to a non-significant change in the 1-AIT group (p=0.053). However no significant difference between the groups was observed (p=0.58). Blood variables measured showed decreasing trends in the 1-AIT group whereas for most variables 4-AIT was necessary to give significant changes. No significant group differences in blood variables were observed. The results from the present study were in accordance with our hypothesis which anticipated that both interventions performed 3 times a week for 10 weeks would induce similar changes in endothelial function and cardiovascular risk factors.