U.S. Population-referenced Percentiles for Wrist-Worn Accelerometer-derived Activity.

Purpose To present age- and sex- specific percentiles for daily wrist-worn movement metrics in U.S. youth and adults. This metric represents a summary of all recorded movement, regardless of the purpose, context, or intensity. Methods Wrist-worn accelerometer data from the combined 2011-2014 National Health and Nutrition Examination Survey (NHANES) cycles and the 2012 NHANES National Youth Fitness Survey (NNYFS) were used for this analysis. Monitor-Independent Movement Summary units (MIMS-units) from raw triaxial accelerometer data were used. We removed the partial first and last assessment days and days with ≥5% non-wear time. Participants with ≥1 valid day were included. Mean MIMS-units were calculated across all valid days. Percentile tables and smoothed curves of daily MIMS-units were calculated for each age and sex using Generalized Additive Models for Location Shape and Scale (GAMLSS). Results The analytical sample included 14,705 participants ages ≥3 years. The MIMS-unit activity among youth was similar for both sexes while adult females generally had higher MIMS-unit activity than males. Median daily MIMS-units peaked at age 6 for both sexes (males: 20,613; females: 20,706). Lowest activity was observed for males and females 80+ years of age; 8,799 and 9,503, respectively. Conclusion Population referenced MIMS-unit percentiles for U.S. youth and adults are a novel means of characterizing total activity volume. By using MIMS-units, we provide a standardized reference that can be applied across various wrist-worn accelerometer devices. Further work is needed to link these metrics to activity intensity categories and health outcomes.