The Ability of Monitor-Independent Movement Summary Units, Euclidean Norm Minus One, and Mean Amplitude Deviation to Harmonize Accelerometry Data Across Research-Grade and Consumer Wearable Devices During Simulated Free-Living Physical Activity in Children

Background: Epoch-level accelerometry summary metrics have the potential to be device-agnostic, meaning that similar estimates should be obtained regardless of the device used. The objective of this study was to identify which metric (Euclidean Norm Minus One [ENMO], mean amplitude deviation [MAD], and Monitor-Independent Movement Summary [MIMS] units) best harmonizes data across devices in an applied setting measuring children’s activity. Methods: Children (n = 239; 9.3 ± 2.1 years, 47% female, 30% Black) wore ActiGraph GT9X (+/−8 g, 50 Hz) accelerometers and were randomized to wear two of three consumer wearables, including Apple Watch Series 7 (+/−16 g, 50 Hz), Garmin Vivoactive 4S (+/−8 g, 25 Hz), and Fitbit Sense (+/−4 g, 50 Hz) on their nondominant wrist while participating in 60 min of simulated free-living activities (i.e., walking, running, and soccer). The standard deviation across z scores for ENMO, MAD, and MIMS of each device was calculated at the second level to quantify variability across devices. Lin’s concordance correlation coefficient was calculated for each combination of devices by metric to determine agreement. Multilevel intraclass correlation coefficients were additionally used to quantify harmonization. Results: The standard deviation of z score across devices was the lowest, indicating better harmonization, for MAD (0.13 ± 0.23), followed by ENMO (0.24 ± 0.50), and then MIMS (0.26 ± 0.39). Lin’s concordance correlation coefficient was strongest for MAD, with coefficients ranging from .89 to .96. Lin’s concordance correlation coefficient for MIMS ranged from .70 to .83 and was lowest for ENMO, ranging from .62 to .76. Overall intraclass correlation coefficient was highest for MAD (.88), followed by MIMS (.73), and ENMO (.62). Conclusions: MAD appears to perform best at harmonizing across all the sampled research-grade and consumer devices in children.