Most studies that explored the health benefits of interrupting sitting time focused on using different modalities (i.e., comparing walking vs standing breaks). However, experimental studies that directly compare patterns of interrupting sitting time through standing only are needed to advance the field. This study aimed to (i) determine if there is a difference in glucose response between continuous sitting (CS) and two intermittent standing regimes (high frequency, low duration breaks (HFLD) and low frequency, high duration breaks (LFHD)) and (ii) to determine if there is a difference in glucose response between the two strategies (HFLD vs. LFHD).
A. Study Participants and Recruitment The target participants were sedentary office employees with impaired fasting glucose level. Participants were recruited through a study flyer via various recruitment channels (i.e., ASU faculty website, social media, word of mouth). The study flyer contains a link to a Qualtrics survey to pre-screen interested participants. All eligible participants will be scheduled for a 30-minute screening visit to assess fasting glucose level. A total of 12 sedentary and inactive employees (indicated by \>6 hrs of workplace sedentary time assessed by the activPAL device during a one-week screening period) will be enrolled to participate in a fully randomized crossover trial.
B. Study Design The study design is a crossover randomized trial with three conditions: (i) uninterrupted sitting, (ii) high-frequency and low duration (HFLD) standing breaks, and (iii) low-frequency and high duration (LFHD) standing breaks. In the interrupted sitting conditions (i.e., HFLD and LFHD), total sitting and standing time were designed to be equal in both groups. The only difference between the two conditions was on the pattern to accumulate sitting time. A common threshold for prolonged sitting time in epidemiological studies of sedentary behavior is 30 minutes of continuous sitting. In the HFLD condition, we will use half of this threshold and ask participants to interrupt their sitting time every 15 minutes using a 2.5-minute standing break. In contrast, participants will perform twice this threshold in the LFHD standing breaks where they will complete a 10-minute standing break every hour of sitting.
All possible sequence of condition were determined and organized into blocks (a total of six blocks). Each eligible participant will be randomly assigned to a block to determine the sequence that they would perform the conditions. The randomization process will involve a separate research staff preparing 40 sealed envelope that contains a block number randomly determined using a computer-generated random sequence. These envelopes will be kept in a secure cabinet by another research staff not directly involved in the project. Each participant will be blinded to the condition that they are going to perform during the visit until after their first standardized meal.
Participants will be invited to three 450-minute (7.5-hour) laboratory visits where they will be provided with a private room, a sit-stand workstation, and a desktop computer. During each laboratory visit, participants will perform their usual desk-based work activities. All visits will be scheduled one week apart. Participants will be instructed to fast overnight, and standardized breakfast and lunch meals will also be provided to control for any dietary effects on glucose level. In addition, each participant will be instructed to avoid any moderate-vigorous physical activities for at least two days and smoking cigarettes and consuming alcoholic beverages at least three days prior to each visit. Upon arrival to the lab for their first visit, participants will complete a dietary log of their last meal the previous day. They will then be instructed to replicate this meal the night prior to each visit.
C. Outcome Measures Continuous Glucose Monitors. A day prior to the first visit, participants will be fitted with a Freestyle Libre Pro (Abbott Laboratories, Chicago, IL) continuous glucose monitor by a trained researcher. The sensor will be attached to the back part of the participant's non-dominant arm and programmed to measure interstitial glucose at 15-minute intervals. The device is designed to be worn continuously for 14 days and is waterproof, lightweight (roughly the size of a quarter) and minimally obtrusive. The sensors will be attached using proper aseptic procedures and in accordance with the manufacturer's instructions. Lastly, each participant will be given instructions on how to care for the device.
At the end of the last visit, data from each sensor will be acquired using the Libre Pro reader and uploaded to an online patient repository (LibreView). Data will then be processed, and 15-minute epoch data will be downloaded into a local secure drive for further processing. Continuous glucose data corresponding to each visit date and time will be isolated using the paper logs and inspected for completeness and quality of data. Files with less than 80% of valid observation will be excluded from the succeeding analyses. Glucose incremental area under the curve (iAUC) will be calculated using the trapezoidal method along with other metrics for variability (i.e., MAGE: mean amplitude of glycemic excursions).
activPAL Device. Objective measures of sitting, standing and moving time will derived from the activPAL micro accelerometer worn on the midline of the right thigh. Participants will wear the device on two occasions: (i) for 7 consecutive days during the baseline period and (ii) for 14 consecutive days during the study. The validity and reliability of the activPAL in measuring sedentary and physical activity behaviors has been previously reported. Collected data will be processed into events of sitting, standing, or moving (i.e., stepping) using the activPAL software version 7.2.32 (PAL Technologies Ltd, Scotland, UK).
Standard Meals. Standardized meals (breakfast and lunch) will be provided in each lab visit to control for any dietary influence. Each meal are designed to provide 33% of the participant's total daily caloric needs following a typical American diet (50-60% carbohydrates, 25-35% fat, and 10-20% protein). Basal metabolic rate will be calculated for each particiapnt using Schofield's equation using a 1.5 activity factor. After calculating the required caloric content of each meal, a meal with the closest caloric value will be chosen from a list of pre-determined meal plan. A typical breakfast will be composed of a croissant, ham, cheddar cheese, cereals with milk, fruit cup, and orange juice while lunch items consisted of a ciabatta ham and cheese sandwich and orange juice. The same meal will be provided during all follow-up visits.
