Abstract 032: Uninterrupted Sitting Induces Unfavorable Changes In Resting Hemodynamics And Inflammatory And Vascular Biomarkers In Physically Inactive And Active Adults
Authors: Nelson Megan C , Casanova Madeline P , Ball Jennavere R , Midence Rachel D , Johnson Timothy R , Martin Bryn , Drum Scott N , Fehrenkamp Bethaney D , Baker Russell T , Vella Chantal A 
Published: May 2021

Introduction:
A single bout of uninterrupted sitting impairs vascular function in the legs, which may be due to reductions in blood flow and shear stress. Participating in regular moderate-to-vigorous physical activity (MVPA) has been identified as an effective approach for improving vascular function, and recent evidence suggests meeting the physical activity (PA) guidelines may attenuate some of the negative health outcomes associated with excessive sedentary behavior; however, it is not well understood how meeting the PA guidelines may influence the acute response to sitting. Our aim was to investigate the effects of 3 h of uninterrupted sitting on hemodynamics and vascular and inflammatory biomarkers in physically inactive and active adults.

Hypothesis:
We hypothesized active adults would experience less detrimental physiological changes after sitting compared to inactive adults.

Methods:
Eleven inactive (mean±SD, age: 47.1±8.9 y, body fat: 33.1±8.5%; 78.5% women) and 16 active adults (age: 46.1±8.9 y, body fat: 25.2±7.2%; 31.1% women) completed 3 h of uninterrupted sitting. Adults self-reported their PA with the International PA Questionnaire. Adults engaging in ≥150 min·wk
-1
were classified as active and <150 min·wk
-1
, inactive. Hemodynamic variables, and superficial femoral artery (SFA) diameter and blood velocity were measured each hour over 3 h of sitting. Mean arterial pressure, blood flow and shear rate were calculated. Serum vascular and inflammatory biomarkers were measured pre and post sitting. Linear mixed-effects modeling was used to assess changes in dependent variables over time and between inactive and active adults, controlling for sex.

Results:
Inactive and active adults self-reported 7.3±7.1 and 93.3±64.8 min·d
-1
of MVPA, respectively. Endothelin-1 (baseline: 8.3±13.4 pg/mL, post: 81.1±103.0 pg/mL; p<0.001) and interleukin-6 (baseline: 0.08±0.06 pg/mL, post: 0.11±0.11 pg/mL; p=0.03) increased post sitting compared to baseline in all adults, regardless of PA status. Systolic blood pressure, mean arterial pressure, calf circumference, and SFA diameter, blood velocity, and mean blood flow decreased over time in both groups (p<0.05 for all). There was an interaction effect for mean shear rate (p=0.008); inactive adults experienced a decline over 3 h of sitting (baseline: 76.1±48.2 s
-1
; 1 h: 55.0±27.4 s
-1
; 2 h: 45.3±24.2 s
-1
; 3 h: 40.8±25.5 s
-1
) while active participants demonstrated no change (baseline: 36.6±21.4 s
-1
; 1 h: 28.1±21.4 s
-1
; 2 h: 26.1±20.9 s
-1
; 3 h: 23.8±19.5 s
-1
). Inactive adults also had a higher oscillatory shear index compared to active adults (p<0.001).

Conclusion:
Uninterrupted sitting induced unfavorable changes regardless of PA status; however, active adults demonstrated a more favorable shear profile. Meeting PA guidelines may attenuate some unfavorable changes within the vasculature associated with prolonged sitting.