Validity and Interrater Reliability of the Fibion Pocket-Worn Device in Laboratory Settings

Background : Accurate and reliable measurements of activity type and intensity are important for monitoring health and well-being. Purpose : Determine the validity and interrater reliability of the pocket-worn Fibion device for classifying activity type and intensity in a laboratory setting. Methods : Forty-nine participants (22.6 ± 4.5 years, 56% male) wore a Fibion in each pocket (dominant and nondominant) while performing approximately 10 activities for 5 min each. To assess validity, classification accuracy for Fibion-predicted activity type (sitting, standing, walking, cycling, and high intensity) and intensity (sedentary, light, and moderate to vigorous) were compared with direct observation using percent agreement and kappa at both the epoch and activity levels. To assess interdevice reliability, predicted activity type and intensity for each epoch and activity were compared between devices worn in the dominant and nondominant pockets using percent agreement, kappa, equivalence testing, linear mixed models, and correlations. Results : For validity, classification accuracies for single activities ranged from 1.0% to 98.1% and 0.5% to 95.0% for activity type and 22.7% to 98.1% and 10.3% to 98.8% for intensity for dominant and nondominant devices, respectively. For interdevice reliability, there were no significant differences in time spent in any activity type or intensity between the two devices. Activity- and epoch-level correlations were moderate to high for all variables ( r  = .56–.99) except for cycling ( r  = .32). Conclusion : In the laboratory, pocket-worn Fibion devices accurately classified sitting, walking at lower speeds, stair climbing, running activities, and most sedentary and moderate to vigorous activity intensities and had moderate-to-high interdevice reliability for all activity types except for cycling.