Comparison Of Outcomes Between Raw Acceleration And Counts-based Methods For Processing Wrist-worn Accelerometers

Evolution of accelerometry-based activity monitors has led to novel processing techniques of raw acceleration data collected at the wrist as opposed to the waist. However, few analyses have compared accelerometer-based activity estimates between emerging wrist thresholds. PURPOSE: The purpose was to compare moderate to vigorous physical activity (MVPA) time and prevalence of meeting youth physical activity guidelines (PAG) when using intensity thresholds for raw acceleration versus activity counts data. METHODS: Data are from the National Cancer Institute’s FLASHE study: a cross-sectional, surveillance study of youth/family behaviors related to cancer prevention. A sub-sample of 409 adolescents (11-17yrs; 50% female) wore an Actigraph GT3X+ monitor on the wrist over 7 days to provide objective data on physical activity. ActiLife software (version 6.10.2) was used to download all data. Raw data were processed with the R package GGIR and associated Hildebrand millig (mg) cut points. Counts data were processed using both Crouter and Chandler cut-points for vertical axis (VA) and vector magnitude (VM). MVPA was defined as METs ≥4. To compare the different processing techniques, differences in MVPA time and adherence to the youth PAG were evaluated using repeated ANOVAs with Bonferroni adjustments and Kappa statistics, respectively. RESULTS: The Hildebrand cut points yielded significantly fewer minutes of MVPA (M±SD: 10.6 ±14.7 min/d) compared to estimates from the Crouter cutpoints (107.3±56.4min/d for VA; 126.4±63.4min/d for VM) and Chandler cutpoints (52.3±34.3min/d for VA; 67.3±40.8min/d for VM): p-values <0.0001 for all comparisons. The prevalence of children meeting the PAG was 0% with Hilldebrand, but ranged substantially from 7% with Chandler VA to 64% with Crouter VM with the counts data. The mg method and counts methods showed very low classification agreement for the PAG (i.e. Kappa ranges from 0.01 to 0.06). Similar patterns were found when analyses were stratified by sex and weight status. CONCLUSIONS: Large discrepancies in MVPA estimates and PAG adherence rates were observed between the raw and counts data processing techniques. Using these different threshold-based methods may lead to disparate conclusions about youth behavior patterns and their relationships with health indicators.