Comparing Two Generations of ActiGraph Accelerometers

Abstract

PURPOSE: To examine the comparability of the ActiGraph 7164 uniaxial accelerometer and the ActiGraph wGT3X-BT triaxial accelerometer (low frequency extension) in wear time, count based estimates (vertical axis), and average time/day in physical activity of different intensities. METHODS: Data are from 87 CARDIA participants, aged 48-60 years, who simultaneously wore the 7164 and wGT3X-BT accelerometers at the waist in 2015-16, with wear time ≥4 of 7 days, ≥10 hr/day. Freedson adult cut points (ct/min) were used to define sedentary (<100), light (100-1951), moderate (1952-5724), and vigorous activity (≥5725). Paired difference tests were used to compare mean or median values between the two accelerometers. Agreement was evaluated using intraclass correlation coefficients and Bland-Altman plots. A calibration formula applied to the wGT3X-BT values was obtained by linear regression. RESULTS: Minute by minute within-person correlations of ct/min/day averaged r=0.74, despite the ≥10 year age of the 7164 devices. Total recorded wear time min/day was nearly identical between the 7164 and wGT3X-BT (881.5 ± 70.9 vs. 880.3 ± 78.1, p=0.72). Linear regression of the wGT3X-BT on the 7164 ct/min/day passed very close to the origin; therefore, the slope of the 7164 ct/min/day (1.088) was the calibration proportionality. After calibrating the wGT3X-BT values (dividing by 1.088), no differences were observed between the 7164 and wGT3X-BT in total accelerometer ct/day (310,184 ± 129,189 vs. 307,085 ± 135,362, p=0.48), average ct/min/day (349.5 ± 139.5 vs. 346.5 ± 147.2, p = 0.54), sedentary (513.2 ± 93.6 vs. 509.6 ± 98.6, p=0.23), light (335.3 ± 81.5 vs. 338.7 ± 81.1, p=0.22), or moderate min/day (31.0 ± 21.9 vs. 30.3 ± 23.4, p=0.31). A significant difference was observed for vigorous min/day in the total sample (0.2 ± 1.0 vs. 0.0 ± 0.3, p<0.01), and also among those with >0 vigorous min/day (N=28, 2.8 ± 4.5 vs. 1.3 ± 2.9, p=0.01). Intraclass correlation coefficients showed excellent agreement for all measures (ICC range = 0.97-0.99). Bland-Altman plots demonstrated acceptable levels of agreement. CONCLUSIONS: After applying a calibration formula, the 7164 and wGT3X-BT are comparable for total wear time, count based estimates, and average min/day in sedentary, light, and moderate activity, but not for vigorous activity.