Acute glucoregulatory and vascular outcomes of three strategies for interrupting prolonged sitting time in postmenopausal women: A pilot, laboratory-based, randomized, controlled, 4-condition, 4-period crossover trial.

Background: Prolonged sitting is associated with cardiometabolic and vascular disease. Despite emerging evidence regarding the acute health benefits of interrupting prolonged sitting time, the effectiveness of different modalities in older adults (who sit the most) is unclear.Methods: In preparation for a future randomized controlled trial, we enrolled 10 sedentary, overweight or obese, postmenopausal women (mean age 66 years ±9; mean body mass index 30.6 kg/m2 ±4.2) in a 4-condition, 4-period crossover feasibility pilot study in San Diego to test 3 different sitting interruption modalities designed to improve glucoregulatory and vascular outcomes compared to a prolonged sitting control condition. The interruption modalities included: a) 2 minutes standing every 20 minutes; b) 2 minutes walking every hour; and c) 10 minutes standing every hour. During each 5-hr condition, participants consumed two identical, standardized meals. Blood samples, blood pressure, and heart rate were collected every 30 minutes. Endothelial function of the superficial femoral artery was measured at baseline and end of each 5-hr condition using flow-mediated dilation (FMD). Participants completed each condition on separate days, in randomized order. This feasibility pilot study was not powered to detect statistically significant differences in the various outcomes, however, analytic methods (mixed models) were used to test statistical significance within the small sample size.Results: Nine participants completed all 4 study visits, one participant completed 3 study visits and then was lost to follow up. Net incremental area under the curve (iAUC) values for postprandial plasma glucose and insulin during the 5-hr sitting interruption conditions were not significantly different compared to the control condition. Exploratory analyses revealed that the 2-minute standing every 20 minutes and the 2-minute walking every hour conditions were associated with a significantly lower glycemic response to the second meal compared to the first meal (i.e., condition-matched 2-hour post-lunch glucose iAUC was lower than 2-hour post-breakfast glucose iAUC) that withstood Bonferroni correction (p = 0.0024 and p = 0.0084, respectively). Using allometrically scaled data, the 10-minute standing every hour condition resulted in an improved FMD response, which was significantly greater than the control condition after Bonferroni correction (p = 0.0033).Conclusion: This study suggests that brief interruptions in prolonged sitting time have modality-specific glucoregulatory and vascular benefits and are feasible in an older adult population. Larger laboratory and real-world intervention studies of pragmatic and effective methods to change sitting habits are needed.ClinicalTrials.gov NCT02743286

BP and heart rate during sitting conditions.

<p>SBP (Panel A), DBP (Panel B), and heart rate (Panel C) measurements at each time point. Panel D. Average iAUC for DBP values across the entire 5-hr sitting period. <i>p</i>-value vs. control condition. Bonferroni-corrected cut-off for significance in 3-arm comparison with control was p< 0.0167. All data are means +/- SEM; n = 10 for the control, 2-minute walking every hour, and 10-minute standing every hour conditions; n = 9 for the 2-minute standing every 20 minutes condition.</p

Glucose and insulin measurements during sitting conditions.

<p>Glucose (Panel A) and insulin (Panel B) concentrations at each time point. Average iAUC for postprandial glucose (Panel C) and insulin (Panel D) responses across the entire 5-hr sitting period for each interruption condition was compared to the control condition. Unadjusted p-values shown only for the comparison involving the 2-minute standing every 20 minutes condition. Bonferroni-corrected cut-off for significance in 3-arm comparison with control was <i>p</i>< 0.0167. All data shown are means +/- SEM; n = 10 for the control, 2-minute walking every hour, and 10-minute standing every hour conditions; n = 9 for the 2-minute standing every 20 minutes condition; M₁ –breakfast meal, M₂ –lunch meal.</p

Change in FMD during sitting conditions.

<p>Condition-associated change in FMD is represented by the ratio of FMD 2 (end of sitting period) to FMD 1 (baseline) and are shown by group (Panels A and B) and by individual (Panels C and D) using raw data (Panels A and C) and allometrically scaled data (Panels B and D) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188544#sec007" target="_blank">Materials and Methods</a> section). An FMD 2–to–FMD 1 ratio greater than 1 (dotted, horizontal line) indicates that the FMD response was greater at the completion of the sitting period relative to baseline. Box and whisker plots (Panels A and B): x = mean, line = median, dots above boxes are outliers. n = 10 for the control, 2-minute walking every hour, and 10-minute standing every hour conditions; n = 9 for the 2-minute standing every 20 minutes condition. <i>p</i>-value vs. the control condition. * Statistically significant after Bonferroni correction. Bonferroni-corrected cut-off for significance in 3-arm comparison with control was <i>p</i>< 0.0167.</p

Clinical characteristics (n = 10).

<p>Clinical characteristics (n = 10).</p

Sitting study design.

<p>Panel A. Schedule of participant study visits. Conditions A, B, C, or D were conducted in random order on Visits 2–5. Panel B. Schematic of sitting condition protocols’ activities. Horizontal black lines indicate the 1-hr lead-in sitting phase to achieve steady state. Vertical bars indicate sitting interruption events for respective conditions during the 5-hr sitting period. All conditions (A-D) included a single, per-protocol bathroom break at study period time 2.5hr. Sitting period time “0 hr” occurred immediately following P2 and B2, the moment when the breakfast standardized meal (M₁) was initiated. M–standardized meal, B–blood collection, P–blood pressure and heart rate collection, F–FMD study, U–bathroom break.</p