Physical Activity Category Classification Using The Actigraph Gt9x In Youth

Abstract

The ActiGraph GT9X includes an inertial measurement unit (IMU) equipped with a triaxial gyroscope which has been shown to be a perfect classifier of sedentary behavior (SB) in adults. To date, there has been no research to explore the application of the gyroscope in youth. PURPOSE: The purpose of this study was to compare the use of the accelerometer and gyroscope for classifying SB and continuous walking and running (CWR) in youth. METHODS: Participants (N=52, mean±SD; age, 13.3±3.1 years; BMI, 20.5±5.0 kg/m2) completed sixteen activities ranging from SB to vigorous intensity. Activities were grouped as SB (lying, computer gaming, internet, reclining, and book reading), CWR (fast over-ground walking, slow over-ground walking, and over-ground running), and intermittent activities (e.g. stair walking, sweeping, stationary cycling, basketball). A GT9X was worn on the right hip, both wrists, and both ankles. Primary accelerometer data were sampled at 90 Hz and converted to the Euclidean norm minus one (ENMO) in milli-G’s per second. Gyroscope data were sampled at 100 Hz and converted to vector magnitude (GVM) and reported in mean degrees per second. ENMO and GVM were assessed for classifying the following: 1). SB from all other activities and 2). SB first, then CWR from the remaining 11 activities using the mean coefficient of variation (CV) per 10-s. Thresholds were developed using receiver operating characteristics (ROC) Performance was assessed using area under the curve (AUC), sensitivity, and specificity. Performance RESULTS: ENMO and GVM classify SB well across all attachment sites (AUC ≥ 95.7%). When classifying CWR after removing SB, ENMO CV had AUC between 85.0%-87.9%, while GVM was lower and more variable with AUC between 53.3%-74.7%. CONCLUSION: Overall, ENMO and GVM are excellent classifiers of SB in youth across all attachment sites. GVM is less effective than ENMO for classifying CWR, but has potential for future use and should continue to be explored.Table: No title available.