Comparison of outcomes derived from the ActiGraph GT3X+ and the Axivity AX3 accelerometer to objectively measure 24-hour movement behaviors in adults : a cross-sectional study

The aim of this cross-sectional study is to investigate convergent validity of outcomes derived from the ActiGraph GT3X and Axivity accelerometer and to investigate feasibility and acceptability of using outcomes derived from these devices to measure 24-h movement behaviors (i.e., sleep, sedentary behavior, and physical activity) in adults during free-living conditions. Twenty-four adults (33.3% male; 39.79 +/- 13.09 years old) simultaneously wore a hip-mounted ActiGraph and thigh-mounted Axivity during 48 consecutive hours. The ActiGraph was switched from hip to wrist during the night. To assess convergent validity between the two devices, Paired sample t-tests, linear regressions, Bland-Altman plots and kappa statistic were conducted. Feasibility and acceptability of the devices was self-reported on a five-point scale. Daily time spent in 24-h movement behaviors differed between both devices. Except for sleep, the mean differences in daily time spent in the behaviors were clinically relevant and the limits of agreement were wide. For all 24-h movement behaviors, except for sleep and vigorous physical activity, proportional errors were observed. kappa statistic showed substantial agreement for total physical activity and outstanding agreement for sedentary behavior and sleep. Adults perceived the Axivity as more practical than the ActiGraph to wear it for more than two days whereas the feasibility to wear it for two days was comparable. Depending on the measure, the observed biases were clinically relevant, proportional to the size of the measure and/or erratically variable. When taking into account the data processing approaches applied in this study, the ActiGraph and the Axivity cannot be used interchangeably to measure 24-h movement behaviors since the bias between both devices is clinically relevant and unpredictable