Characteristics of a Protocol to Collect Objective Physical Activity/Sedentary Behavior Data in a Large Study: Seniors USP (Understanding Sedentary Patterns)

The Seniors USP (Understanding Sedentary Patterns) study measured sedentary behavior (activPAL3, 9-day wear) in older adults. The measurement protocol had three key characteristics: enabling 24-hour wear (monitor location, waterproofing), minimizing data loss (reducing monitor failure, staff training, communication), and quality assurance (removal by researcher, confidence about wear). Two monitors were not returned; 91% (n = 700) of returned monitors had seven valid days of data. Sources of data loss included monitor failure (n = 11), exclusion after quality assurance (n = 5), early removal for skin irritation (n = 8), or procedural errors (n = 10). Objective measurement of physical activity and sedentary behavior in large studies requires decisional trade-offs between data quantity (collecting representative data) and utility (derived outcomes that reflect actual behavior).