Abstract
The objective of this study was to compare acute effects of prolonged sitting, prolonged standing and sitting interrupted with regular activity breaks on vascular function and postprandial glucose metabolism. In a randomized cross-over trial, 18 adults completed: 1. Prolonged Sitting; 2. Prolonged Standing and 3. Sitting with 2-min walking (5 km/h, 10% incline) every 30 min (Regular Activity Breaks). Flow mediated dilation (FMD) was measured in the popliteal artery at baseline and 6 h. Popliteal artery hemodynamics, and postprandial plasma glucose and insulin were measured over 6 h. Neither raw nor allometrically-scaled FMD showed an intervention effect (p = 0.285 and 0.159 respectively). Compared to Prolonged Sitting, Regular Activity Breaks increased blood flow (overall effect of intervention p<0.001; difference = 80%; 95% CI 34 to 125%; p = 0.001) and net shear rate (overall effect of intervention p<0.001; difference = 72%; 95% CI 30 to 114%; p = 0.001) at 60 min. These differences were then maintained for the entire 6 h. Prolonged Standing increased blood flow at 60 min only (overall effect of intervention p<0.001; difference = 62%; 95% CI 28 to 97%; p = 0.001). Regular Activity Breaks decreased insulin incremental area under the curve (iAUC) when compared to both Prolonged Sitting (overall effect of intervention P = 0.001; difference = 28%; 95% CI 14 to 38%; p<0.01) and Prolonged Standing (difference = 19%; 95% CI 4 to 32%, p = 0.015). There was no intervention effect on glucose iAUC or total AUC (p = 0.254 and 0.450, respectively). In normal-weight participants, Regular Activity Breaks induce increases in blood flow, shear stress and improvements in postprandial metabolism that are associated with beneficial adaptations. Physical activity and sedentary behaviour messages should perhaps focus more on the importance of frequent movement rather than simply replacing sitting with standing.
Highlights
Sedentary behaviour is associated with increased risk of mortality, cardiovascular disease and type 2 diabetes [1, 2], but regular high levels (e.g. >60 min) of moderate-to-vigorous physical activity may prevent such associations [3]
Regular Activity Breaks decreased insulin incremental area under the curve when compared to both Prolonged Sitting and Prolonged Standing
A growing number of studies have been conducted in this area, confirming that ~1.5 min– 5 min of light or moderate activity performed every 20–30 min can improve postprandial glucose metabolism when compared to 2–9 h of uninterrupted sitting in participants ranging from obese type 2 diabetics to healthy inactive young adults [4,5,6,7]
Summary
Sedentary behaviour (performing activities when sitting or lying that involve < 1.5 MET of energy usage) is associated with increased risk of mortality, cardiovascular disease and type 2 diabetes [1, 2], but regular high levels (e.g. >60 min) of moderate-to-vigorous physical activity may prevent such associations [3]. Most intervention studies designed to test the causality of the association between sedentary behaviour and health outcomes have focused on the acute effects of regularly interrupting periods of prolonged sitting with short bouts of activity on postprandial metabolism. The results of the small number of acute studies conducted indicate that short bouts of standing [8], or even alternating 30 min of standing with 30 min of sitting [9], are not as effective at reducing postprandial glycemia as regular activity breaks, in healthy, normal weight populations [8]. Changes in circumferential pressure and shear stress (the forces associated with blood flow) play an important role in the prevention or development of endothelial dysfunction and atherosclerosis [14]. The aim of this study was to compare the effects of prolonged sitting, prolonged standing and sitting interrupted with regular activity breaks on endothelial function and postprandial glycemic response
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