Study design and participants
Randomized cross-over study design was used to compare two different types of standing interventions. A total of twelve obese and overweight (BMI above 25 and less than 40 kg/m2) older participants (age range = 65-78 years) with clinically confirmed T2DM were recruited from flyers available to previous University ---BLINDED TEXT--- research participants. Four participants reported their daily sitting rates as less than 6 hours/day, while eight rated their daily sitting duration between 6-10 hours/day. Participants' demographic and clinical characteristics are presented in table 1. All subjects completed a 3-hour sitting session prior to randomization to the cross-over study. All participants underwent a short clinical and motor function test battery pre- and post-study.
-- Please insert Table 1 about here --
Ethics:
---BLINDED TEXT---
Study protocol
Participants stood behind a height adjustable table that was positioned about 0.5 meters from a wall and ergonomically adjusted to each individual, in agreement with the United States Department of Labor - Occupational Safety and Health Administration (OSHA) recommendations (OSHA, n.d.-a). For the “static standing” position participants were asked to stand behind the table and there were no specific restrictions imposed for standing (e.g. “do not move” or “stand quietly”). For the “dynamic standing” condition participants stood behind the same table. The table top made small (in the order of approximately 30-50 cm or less) lateral movements that facilitated participants to make small steps. In both conditions, participants were allowed to shift their weight as often as desired with instructions to stand close to the tabletop. Leaning on the tabletop was permitted. Each standing session did not exceed 4 hoursParticipants stood on an anti-fatigue mat during each of the standing sessions.
A seated control session condition was also used to get baseline measures for the primary variable (resting state VO2 consumption). The seated session did not exceed 3 hours and participants remained seated throughout the test period except for the rare break.
The experimental testing protocol was conducted over three separate days, with each test day dedicated to one of the testing conditions. The sitting (baseline) condition was conducted first by all participants, followed by either static or dynamic condition (randomly assigned). For each of the conditions as many rest breaks were provided to the participants as needed. The same test battery was administered during each of the conditions.
Standing Desk
To facilitate dynamic standing, a custom-built dynamic standing workstation was used. This workstation consisted of a height-adjustable desk with a tabletop that oscillated slowly in the transverse plane, medio-laterally, by means of a linear actuator.
Instrumentation
Descriptive measures of user behavior and experience of table use
Number and duration of breaks taken during sitting and standing conditions
Participants could alternate between standing and sitting down ad libitum. Total time spent standing and sitting and the number, nature, and duration of breaks were recorded.
Total movements
During all three conditions participants wore a tri-axial accelerometer (Actigraph GT3X+, Actigraph Inc., Florida, USA), which was placed at the right side of the hip. Participants’ activity was recorded at 30 Hz and aggregated to 10-s epochs. Raw accelerometer activity counts were first manually cleaned, eliminating time periods spent on breaks, and further processed in MATLAB®.
Musculoskeletal discomfort rates
Participants were asked to report musculoskeletal discomfort at the beginning and then every 30 minutes using a 100-mm visual analogue scale. Specifically, the participants indicated the location of the discomfort by marking an ‘X’ on a drawing of a human body, as well as its severity by drawing a vertical line along a horizontal line beginning at “No discomfort at all” and ending at “Worst discomfort ever experienced” [15]. Discomfort was quantified on this visual analogue scale by measuring the horizontal distance between the first vertical line (i.e., “No discomfort at all”) and the line drawn by the participants, with potential ratings ranging from a minimum of 0 mm to a maximum of 100 mm [16, 17]. This method allows for a more fine-grained rating of musculoskeletal discomfort than e.g. a 10-point visual analogue scale. Any discomfort reported immediately before a standing session was subtracted from subsequently reported discomfort for each body part, with a minimal possible value of 0 mm. For analysis purposes, total discomfort ratings at time points 0, 60, 120, 180 for all three sessions and 240 minutes in the standing session were presented and statistically analyzed.
Leg swelling
Immediately pre- and post-each session, ankle girth of both sides was recorded using a soft tape measure to get an estimate of lower extremity edema. An absolute pre- and post-condition difference of the mean value of left and right ankle girth was reported.
Primary outcome measure: Oxygen Consumption (VO2)
Oxygen consumption of the participants was measured by indirect calorimetry using the Cosmed K4b2 gas analyzer (Cosmed, Rome, Italy). For the sitting condition, a final oxygen uptake was calculated as a mean of four 10-minute measurements taken at time points 1-10 min, 50-60 min, 110-120 min, and 170-180 min. For both static and dynamic standing conditions an additional measurement was taken into consideration at time point 230-240 min.
Secondary outcome measure: Cognitive performance
Two sets of cognitive tests were applied during sitting and both standing sessions. First, the D-KEFS Trail Making Test (TMT) was used to assess set shifting and executive functioning. All five conditions were assessed and the total time taken to complete each of them is presented. TMT-1 measures visual scanning, TMT-2 number sequencing, TMT-3 letter sequencing, TMT-4 number-letter switching, and TMT-5 motor speed [18]. Second, an analog version of the Stroop test (Stroop Color-Word test) was also used [19]Stroop-1 measures word naming/reading, Stroop-2 measures color naming, Stroop-3 measures verbal response inhibition, and Stroop-4 measures inhibition/switching. The time taken was recorded in seconds for each Stroop condition.
Statistical analysis
Data were analyzed in SPSS software version 25.0 (IBM, Armonk NY, USA). Parametric data were entered into a 2x2 mixed design repeated measures analyses of variance (ANOVA) with conditions Sitting, Static standing and Dynamic standing as the within subject variable, with post hoc comparisons carried out with the Bonferroni correction method for multiple testing. Non-parametric data were analyzed with Friedman’s ANOVA. Significant results were further evaluated in post hoc pairwise comparisons using a Wilcoxon Signed-Ranks Matched-Pairs test. Best fit line plotting was performed to determine the rate of total musculoskeletal discomfort development. An alpha below 0.05 indicated statistical significance.