Impact of prolonged sitting on vascular function in young girls.

What is the central question of this study? Children are spending more than 60% of their waking day sedentary. The consequences of excessive sedentary behaviour are not well understood in the child, but there is growing evidence that with increasing sedentary time, cardiovascular risk in childhood also increases. What is the main finding and its importance? Our findings show that a 3 h period of uninterrupted sitting causes a profound (33%) reduction in vascular function in young girls. Importantly, we also demonstrate that breaking up sitting with regular exercise breaks can prevent this. Excessive sedentary behaviour has serious clinical and public health implications; however, the physiological changes that accompany prolonged sitting in the child are not completely understood. Herein, we examined the acute effect a prolonged period of sitting has upon superficial femoral artery function in 7- to 10-year-old girls and the impact of interrupting prolonged sitting with exercise breaks. Superficial femoral artery endothelium-dependent flow-mediated dilatation, total shear rate, anterograde and retrograde shear rates and oscillatory shear index were assessed before and after two experimental conditions: a 3 h uninterrupted period of sitting (SIT) and a 3 h period of sitting interrupted each hour with 10 min of moderate-intensity exercise (EX). A mixed-model analysis of variance was used to compare between-condition and within-condition main effects, controlling for the within-subject nature of the experiment by including random effects for participant. Superficial femoral artery endothelium-dependent flow-mediated dilatation decreased significantly from pre- to post-SIT (mean difference 2.2% flow-mediated dilatation; 95% confidence interval = 0.60-2.94%, P < 0.001). This relative decline of 33% was abolished in the EX intervention. Shear rates were not significantly different within conditions. Our data demonstrate the effectiveness of short but regular exercise breaks in offsetting the detrimental effects of uninterrupted sitting in young girls.