Calibration of wrist-worn ActiWatch 2 and ActiGraph wGT3X for assessment of physical activity in young adults

Background: The validity of Actiwatch 2 in assessing sleep was evident, but its validity in assessing physical activity (PA) level was unknown.
Research question: The objective of this study was to validate the wrist-worn Actiwatch 2 and ActiGraph wGT3X as a measurement of PA level against energy expenditure measured by indirect calorimetry.
Methods: Twenty-seven university students aged 18–26 were recruited from July 2016 to May 2017. They were instructed to run at different speeds (4, 6, 8, 10, and 12 km/h) on a treadmill, each speed for 10 min. Oxygen consumption and carbon dioxide production of the subjects was measured by indirect calorimetry using the Cosmed K4b2 gas analyzer. Each subjects wore a single pair of accelerometers (Actiwatch 2 and ActiGraph wGT3X) on both wrists.
Results: All the accelerometers were strongly correlated (ρ=0.83-0.94, all p-values <0.001), and all four accelerometers were strongly correlated with the METs obtained from the Cosmed K4b2 (ρ=0.72-0.74, all p-values <0.001). Regression analysis showed that the non-dominant wrist-worn Actiwatch 2 cutoff cpm for moderate and vigorous PA were 399 and 1,404, respectively; for the ActiGraph wGT3X-BT the corresponding cutoffs were 4,514 and 15,044, respectively. The goodness-of-fit of the MET prediction equations were all >75%. When classifying the activities as either sedentary, light activity, moderate-intensity activity, or vigorous-intensity activity using the MET prediction equations, the agreements between the four accelerometers and that by the Cosmed K4b2 were high, all AUCs were above 80% except those of the Actiwatch worn on the left (non-dominant) wrist. The Bland-Altman plots show that, for all four accelerometers, the biases were close to zero and error variances were largest when the mean measurements were around 6 METs.
Significance: We showed that wrist-worn Actiwatch 2 and ActiGraph wGT3X-BT were strongly correlated in PA assessment. Copyright © 2018 Elsevier B.V. All rights reserved.