ActiGraph™ activity monitors: "the firmware effect".

Purpose: The objective of this study is to examine the effect of different firmware versions on ActiGraph™ counts from the laboratory, field, and mechanical shaker testing.

Methods: Counts from 5 GT3X and 7 GT1M firmware versions were compared in this study. Monitors uploaded with these firmware versions were worn on the hip by 15 participants (age = 24.9 ± 5.0 yr, BMI= 23.9 ± 2.4 kg · m(-2)) who performed laboratory-based treadmill (walking: 1.5, 3.0 and 4.5 mph; running: 6 mph) and simulated free-living activities (sitting, self-paced walking, filing papers, dusting, vacuuming, and cleaning the room). Testing was also conducted during 1 d of free living and using orbital mechanical shaker testing at 0.7, 1.3, 2.0, and 3.0 Hz. Intermonitor comparisons for vertical, anteroposterior, mediolateral, and triaxial vector magnitude counts were conducted using one-way ANOVA and post hoc pairwise comparisons (P < 0.05).

Results: Vertical counts during treadmill walking at 1.5 mph from the GT1M monitor with firmware version 1.1.0. were significantly greater (P < 0.05; 75%) than output from the monitor with firmware version 1.3.0. Shaker testing revealed statistically significant differences in vertical and lateral counts. Although there were no significant differences among activity counts in the free-living comparisons, firmware version 1.1.0. produced the highest vertical counts during this protocol.

Conclusion: Greater sensitivity of firmware version 1.1.0. to low-frequency sedentary activities resulted in greater counts than other firmware versions. It is recommended that before releasing new firmware, ActiGraph™ perform both human and mechanical shaker testing to verify comparability in outputs between new and previous firmware versions.