Abstract
Accelerometers have been used to objectively quantify physical activity, but they can pose a high burden. This study was conducted to determine the feasibility of using a single-item smartphone-based ecological momentary assessment (EMA) in lieu of accelerometers in long-term assessment of daily exercise. Data were collected from a randomized controlled trial of intermittently exercising, otherwise healthy adults (N = 79; 57% female, mean age: 31.9 ± 9.5 years) over 365 days. Smartphone-based EMA self-reports of exercise entailed daily end-of-day responses about physical activity; the participants also wore a Fitbit device to measure physical activity. The Kappa statistic was used to quantify the agreement between accelerometer-determined (24 min of moderate-to-vigorous physical activity [MVPA] within 30 min) and self-reported exercise. Possible demographic predictors of agreement were assessed. Participants provided an average of 164 ± 87 days of complete data. The average within-person Kappa was κ = 0.30 ± 0.22 (range: -0.15-0.73). Mean Kappa ranged from 0.16 to 0.30 when the accelerometer-based definition of an exercise bout varied in duration from 15 to 30 min of MVPA within any 30 min period. Among the correlates examined, sex was significantly associated with agreement; mean agreement was higher among women (κ = 0.37) than men (κ = 0.20). Agreement between EMA self-reported and accelerometer-measured exercise was fair, suggesting that long-term exercise monitoring through a single-item EMA may be acceptable.