Abstract
The ActiGraph GT3X+ accelerometer’s normal (NR) and low-frequency extension (LFE) filters produce steps/day estimates incongruent with those from previous ActiGraph models or other research-grade pedometers. Using the ActiGraph model 7164, censoring those steps (re-setting steps/min to zero) accumulated at < 500 activity counts/min yields steps/day estimates which more closely approximate those obtained from pedometers. However, the validity of censoring ActiGraph GT3X+ step data has not been evaluated. PURPOSE: To compare free-living steps/day derived from the ActiGraph GT3X+ using the NR filter, LFE filter, and LFE filter + step censoring (censor steps at < 500 activity counts/min) to those obtained from the NL-1000 pedometer. METHODS: Ten adults (40% male, 28.0 ± 2.7 yrs, 23.0 ± 3.8 kg/m2) wore an ActiGraph GT3X+ and an NL-1000 at their waist for 7 days (24 hr/day). A total of 65 days were available for analysis (wear time ≥ 10 hr/day). Linear mixed-effects models were used to evaluate differences in mean steps/day between the NL-1000 and the three different steps/day outputs derived from the ActiGraph GT3X+. Mean absolute percent error (MAPE) was quantified and Bland-Altman analyses were conducted to evaluate step outputs from all three ActiGraph GT3X+ methods in comparison to the NL-1000. RESULTS: Relative to the NL-1000 (8502 ± 456 steps/day), the NR filter underestimated steps (7643 ± 463 steps/day, p < .01), the LFE filter overestimated steps (14266 ± 643 steps/day, p < .01), and the LFE filter + step censoring produced comparable mean values (8559 ± 465 steps/day, p > .05). Values for MAPE (NR filter: 11.5 ± 1.1%; LFE filter: 78.3 ± 6.6%; LFE filter + step censoring: 8.2 ± 1.3%) indicated that the LFE filter + step censoring produced significantly less error than the NR or LFE filters (all p < .05). Bland-Altman analyses suggested the LFE filter + step censoring provided better agreement with the NL-1000 than the NR or LFE filters; however, the limits of agreement were wide for all ActiGraph methods (NR filter: -2317 to 600 steps/day; LFE filter: -1820 to 13387 steps/day; LFE filter + step censoring: -1502 to 1619 steps/day). CONCLUSION: The LFE filter + step censoring method with the ActiGraph GT3X+ yielded steps/day values that more closely approximate outputs obtained from a research-grade pedometer.
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