Evaluation of a disease-specific mHealth-based exercise self-tracking measure

ObjectivesThis study investigates the concurrent and construct validity of a brief, customizable exercise self-tracking item from a research mHealth App ("Phendo") for use as a measure of day-level and habitual exercise behavior in endometriosis. Study SampleStudy 1 included 52 participants who were recruited online and provided data for up to 14 days. Study 2 included 359 Phendo users who had retrospectively-collected data on the study measures. MethodsIn Study 1, we evaluated the responses on the self-tracking exercise item as estimates of day-level moderate-to-vigorous intensity exercise (MVE) and total step counts. Comparison measures included recall-based MVE minutes and accelerometry-based step counts, which were self-reported through daily surveys. In Study 2, we derived a measure of habitual exercise using each individuals longitudinal self-tracked responses. We assessed its concurrent validity using the Nurses Health Study II Physical Activity Scale (NHS-II) as the comparison measure. We assessed its discriminant validity through known-group differences analysis where the sample was dichotomized based on Health Survey Short Form-36 (SF-36) and body mass index (BMI). Data AnalysisWe assessed bivariate associations between the scores on the self-tracking and comparison measures using Kendalls rank correlations. We estimated daily MVE and step counts (Study 1), and weekly exercise (Study 2) from the self-tracking item scores through adjusted linear and polynomial regression models. We used t-tests and linear regression to conduct known-group differences analyses. ResultsIn Study 1, self-tracked exercise responses were moderately correlated with survey based MVE and step counts. Regression analyses indicated that overall exercise responses were associated with [~]17 minutes of MVE for the average participant (B=16.09, t=3.11, p=0.045). Self-tracked aerobic-type exercise was a stronger predictor of MVE minutes and step counts (B=27.561, t=5.561, p<0.0001). In Study 2, each self-tracked exercise instance corresponded to [~]19 minutes of exercise per week on the NHS-II Scale (B=19.80, t=2.1, p=0.028). Finally, there were statistically significant differences between the groups dichotomized based on SF-36 subscale scores and BMI. ConclusionThis study presents preliminary evidence on the concurrent and discriminant validity of a brief mHealth App measure for exercise self-tracking among individuals with endometriosis. These findings have implications in the context of large-scale studies that involve monitoring a diverse group of participants over long durations of time, as well as engaging and retaining research participants.