Effect of different walking break strategies on superficial femoral artery endothelial function

Breaking up prolonged sitting with physical activity (PA) breaks prevents conduit artery dysfunction. However, the optimal break strategy to achieve this, in terms of the frequency or duration of PA, is not known. This study assessed the effect of breaking up sitting with different PA break strategies on lower limb peripheral artery endothelial function. Fifteen participants (10 male, 35.8 +/- 10.2 years, BMI: 25.5 +/- 3.2 kg m(-2)) completed, on separate days, three 4-h conditions in a randomized order: (1) uninterrupted sitting (SIT), (2) sitting with 2-min light-intensity walking breaks every 30 min (2WALK), or (3) sitting with 8-min light-intensity walking breaks every 2 h (8WALK). At baseline and 4 h, superficial femoral artery function (flow-mediated dilation; FMD), blood flow, and shear rate (SR) were assessed using Doppler ultrasound. For each condition, the change in outcome variables was calculated and data were statistically analyzed using a linear mixed model. There was no significant main effect for the change in FMD (P = 0.564). A significant main effect was observed for the change in blood flow (P = 0.022), with post hoc analysis revealing a greater reduction during SIT (-42.7 +/- 14.2 mL center dot min) compared to 8WALK (0.45 +/- 17.7 mL center dot min; P = 0.012). There were no significant main effects for mean, antegrade, or retrograde SR (P > 0.05). Superficial femoral artery blood flow, but not FMD, was reduced following uninterrupted sitting. This decline in blood flow was prevented with longer duration, less frequent walking breaks rather than shorter, more frequent breaks suggesting the dose (duration and frequency) of PA may influence the prevention of sitting-induced decreases in blood flow.