OBJECTIVE: The effects of land-based high-intensity interval training (HIIT) on the cardiovascular system have already been demonstrated. However, the water environment is different from that on land. Therefore, we investigated the effects of 6-week aquatic HIIT and moderate-intensity continuous training (MICT) on central hemodynamic parameters, endothelial function, and aerobic fitness in inactive adults. METHODS: Thirty-one inactive adults were randomly assigned to HIIT or MICT group. HIIT group performed twelve 30-s swimming exercise bouts with the intensity of 95% HRmax and 15 to 18/20 RPE with a 60-s rest period between each bout. MICT group performed a 30-min uninterrupted swimming exercise with the intensity of 70% to 75% HRmax and 12 to 14/20 RPE. Training frequency for both groups was three times a week. The pulse wave analysis and flow-mediated dilation (FMD) were measured by non-invasive equipments. RESULTS: The aerobic fitness significantly increased after HIIT, but no change was seen after MICT. Augmentation pressure (AP) and augmentation index normalized at 75 bpm (AIx@HR75) significantly decreased after HIIT but not MICT, whereas MICT rather than HIIT improved subendocardial viability ratio (SEVR), central and peripheral blood pressure, and resting HR. Only HIIT significantly increased brachial endothelial function. CONCLUSION: A six-week aquatic HIIT and MICT had no differences in hemodynamic parameters, endothelial function, and aerobic fitness, however 6 weeks of aquatic HIIT reduced arterial stiffness, increased endothelial function and aerobic fitness, while 6 weeks of aquatic MICT reduced arterial blood pressure and resting HR and increased the coronary blood flow reserve.

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