Eight weeks of high‐intensity interval training is insufficient to prevent sitting‐induced endothelial dysfunction and microvascular impairment

Abstract Prolonged sitting disrupts lower‐limb endothelial and microvascular function, likely via reduced shear stress and blunted microvascular reactivity. We examined whether Tabata‐style high‐intensity interval training (HIIT) mitigates this sitting‐induced vascular dysfunction. Twenty‐two healthy young adults (age 20.3 ± 0.8 years) were randomly assigned to a control group ( n = 11) or a training group ( n = 11); each group comprised seven men and four women. Participants completed 8 weeks of HIIT (4 sessions/week) using a cycle ergometer and bodyweight exercises. Before and after the intervention, participants underwent a 3 h period of sitting during which popliteal artery flow‐mediated dilation (FMD) and reactive hyperaemic blood flow were assessed; plasma nitrate/nitrite and endothelin‐1 were also measured at rest. Sitting reduced popliteal artery blood flow and shear rate in both groups before and after training ( P < 0.05). Popliteal artery FMD decreased after sitting at baseline in both groups and remained lower after sitting in the training group post‐intervention. However, post‐sitting FMD at week 8 was higher in the HIIT group than in controls after adjustment for pre‐sitting FMD. Post‐sitting blood‐flow area under the curve was decreased by sitting in both groups before and after the intervention ( P < 0.05), and resting nitrate/nitrite and endothelin‐1 did not change with training. These results indicate that 8 weeks of HIIT does not prevent sitting‐induced impairments in endothelial function or microvascular function. Although the HIIT maintained higher post‐sitting FMD, HIIT alone was insufficient to counteract the acute endothelial and microvascular dysfunction imposed by sitting.