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

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.