Prolonged sitting-induced leg endothelial dysfunction is prevented by fidgeting

Abstract

Prolonged sitting impairs endothelial function in the leg vasculature, and this impairment is thought to be largely mediated by a sustained reduction in blood flow-induced shear stress. Indeed, preventing the marked reduction of shear stress during sitting with local heating abolishes the impairment in popliteal artery endothelial function. Herein, we tested the hypothesis that sitting-induced reductions in shear stress and ensuing endothelial dysfunction would be prevented by periodic leg movement, or "fidgeting." In 11 young, healthy subjects, bilateral measurements of popliteal artery flow-mediated dilation (FMD) were performed before and after a 3-h sitting period during which one leg was subjected to intermittent fidgeting (1 min on/4 min off) while the contralateral leg remained still throughout and served as an internal control. Fidgeting produced a pronounced increase in popliteal artery blood flow and shear rate (prefidgeting, 33.7 ± 2.6 s(-1) to immediately postfidgeting, 222.7 ± 28.3 s(-1); mean ± SE; P < 0.001) that tapered off during the following 60 s. Fidgeting did not alter popliteal artery blood flow and shear rate of the contralateral leg, which was subjected to a reduction in blood flow and shear rate throughout the sitting period (presit, 71.7 ± 8.0 s(-1) to 3-h sit, 20.2 ± 2.9 s(-1); P < 0.001). Popliteal artery FMD was impaired after 3 h of sitting in the control leg (presit, 4.5 ± 0.3% to postsit: 1.6 ± 1.1%; P = 0.039) but improved in the fidgeting leg (presit, 3.7 ± 0.6% to postsit, 6.6 ± 1.2%; P = 0.014). Collectively, the present study provides evidence that prolonged sitting-induced leg endothelial dysfunction is preventable with small amounts of leg movement while sitting, likely through the intermittent increases in vascular shear stress.

Keywords: blood flow; endothelial function; leg movement; physical inactivity; sitting.

Fig. 1.

Experimental design. A: schematic diagram of experimental protocol and positional changes over the course of the study. Measurements taken at the time points of 1, 2, and 3 h were made while the subject was in the seated position, whereas presit and postsit measurements were taken while subject was in the supine position. B: expected popliteal artery shear stress stimulus during sitting in the control and fidgeting legs. FMD, flow-mediated dilation.

Fig. 2.

Popliteal artery shear rate in the control and fidgeting legs. A: popliteal artery shear rate before, during, and after sitting for 3 h in the control and fidgeting legs. Basal measurements of popliteal artery shear rate (in both legs) during sitting were performed after 2 min of rest following the 1-min fidgeting. B: popliteal artery shear rate during sitting immediately after fidgeting in the control and fidgeting legs. Measurements of shear rate responses to fidgeting (in both legs) were initiated immediately (within 2 or 3 s) after the fidgeting bout. In the control leg, error bars are within symbols. Data are expressed as means ± SE. *P < 0.05 vs. presit; †P < 0.05, between legs.

Fig. 3.

Popliteal artery FMD in the control and fidgeting legs before and after sitting for 3 h. FMD data are noncorrected for hyperemic shear rate area under the curve. Data are expressed as means ± SE. *P < 0.05 vs. presit; †P < 0.05, between legs.