Accuracy Of A Smartphone-based “App” For The Assessement Of Sedentary And More Active Behaviors

Abstract

Mobile devices provide a convenient platform for log-based assessments of sedentary and physical activity (PA) behaviors. PURPOSE: This study aimed to evaluate the accuracy of a smartphone-based “app” designed to assess context-specific forms of sitting, light-intensity PA (LPA), and moderate-vigorous PA (MVPA). METHODS: Adults (N=23 [323 observations]; 49.0±8.9 years; 85% men; 73% Caucasian; BMI=35.0±8.3kg/m2) reported their sitting, LPA, and MVPA over the course of an 11-week behavioral intervention. During three separate 7d time period, participants simultaneously wore the ActivPAL3c™ accelerometry/inclinometer as a criterion measure. Intraclass correlation (ICC [95% CI]) and bias estimates (mean difference [¯d] and absolute percent error [APE = difference/direct observation x 100]) were used to compare app-based reported behaviors to measure sedentary time (lying/seated position), LPA (standing or stepping < 3 metabolic equivalents [METs], and MVPA (stepping ≥ 3METs). RESULTS: Sitting time accuracy was moderate (ICC=0.50 [0.37, 0.60]) with under-reporting (¯d = -127 [-612.41, -356.73] minutes/day; APE = -8.61 [-155.73, 140.51]). LPA and MVPA time accuracy was also moderate (ICC=0.64 [0.55, .72] and 0.55 [0.32, 0.71], respectively) with over-reporting (¯d = 293.00 [-39.06, 625.06] minutes/day; APE = 31.87 [-138.28, 202.02]) and (¯d = 19.46 [-133.20, 172.12] minutes/day; APE=83.93 [-387.21, -555.07]). CONCLUSION: The smartphone-based log targeting sedentary and more active behaviors underreported sedentary time and overreported LPA and MVPA with only moderate accuracy relative to an objective monitor. This tool may still be useful as a self-monitoring tool in the context of a behavioral intervention as well as a tool to capture context-specific forms of sedentary, LPA, and MVPA behaviors. Given the wide variations in accuracy, future research may explain some reasons for under- or over-reporting of behaviors.