Measures

Participants completed one seven-day diary for each quarter of the study, during which they were asked to code their activities in 15-minute epochs throughout the entire day on seven consecutive days. Codes aligning with sedentary behaviors included: “sitting while: eating, watching television, reading, driving, using computer/smartphone, etc.”. Days with fewer than 10 waking hours reported were considered invalid and excluded from the main analysis. Daily average minutes of sedentary time was calculated as a weighted average for quarters with a minimum of four valid days. Quarterly values were further averaged to generate mean daily minutes of sedentary time which account for seasonal changes in behavior.

During two non-consecutive quarters (Q1/Q3 or Q2/Q4), participants wore an Actigraph GT3x accelerometer on the hip aligning with the midline of the non-dominant thigh. Participants were instructed to wear the device for seven consecutive days concurrent with the seven-day diary during all waking hours, except when bathing or participating in water-based activities. Accelerometer data that was recorded on invalid diary dates were excluded to maintain an overlap in valid accelerometer/diary days.

Raw Actigraph data were processed using the Choi algorithm to calculate accelerometer wear time and the sojourn-3 axis algorithm to estimate daily sedentary time.(27–30) The sojourn-3 axis method is a hybrid machine-learning, neural network, and decision tree analysis algorithm which uses second-by-second triaxial accelerometer counts to estimate free-living sedentary time.(29) Days failing to meet the wear time minimum of 10 hours/day were excluded from the main analysis. Daily average minutes of sedentary time was calculated as a weighted average for quarters with a minimum of four valid days.(31) Quarterly values were further averaged to generate mean daily minutes of sedentary time which account for seasonal changes in behavior.

Participants completed the same four-page survey at the beginning and end of the one-year validation study. Information on sedentary time was collected using the question, “During the past year, estimate the hours per day you spent on typical weekdays and weekends in each of the following activities. Please average your seasonal physical activities over the entire year. Try to account for all 24 hours per day”. Sedentary time items included “sitting or lying down while watching TV” and “other sitting (at work, at computer, while driving, eating, etc.)”, with responses including “0, <1, 1–2, 3–4, 5–6, 7–8, 9–10, 11+ hours per day”. To generate a “total sitting time” value, the mean number of hours within the response categories (i.e. 0, 0.5, 1.5, 3.5, 5.5, etc. hours per day) were summed for the TV-related sedentary time and other sedentary time items.