ABSTRACT: BACKGROUND:Despite the benefits of regular physical activity, women in every age group have lower activity levels than men, and few women meet the recommended levels of physical activity. Digital technologies have been useful in increasing physical activity during the course of an interventional study. However, sustaining that activity once the clinical trial was complete was a major challenge. OBJECTIVE:This study aimed to describe the experiences and perspectives of physically inactive women who completed the mobile phone-based physical activity education (mPED), a randomized controlled trial, at 12 months. METHODS:Of 210 women who were enrolled in the mPED trial, 203 completed a 12-month open-ended exit interview and survey through phone. The participants were asked about their physical activity levels; their digital technology use; what they learned from, liked, and would change about the trial; their motivations to keep active post-trial; and their advice for other women. Interviews were transcribed verbatim and thematically analyzed using the brief survey qualitative description. Descriptive statistics were used to describe the survey data with the significance level set at P<.05. RESULTS:In the 12-month survey, a greater proportion of the participants in the intervention group, compared with the control group, reported that they regularly wore a pedometer or physical activity tracker (49.3%, 66/143 vs 26.1%, 18/69; P=.002) and engaged in brisk walking (54.5%, 73/134 vs 30.4%, 21/69; P=.001). The experiences and perceptions of physical activity of physically inactive women over time were embedded in a complex interplay of internal and external factors. A total of 6 interactive themes emerged as critical in supporting continued engagement in physical activity postintervention: tracking, technology versus personal touch, accountability, resources and environment, motivation, and habit formation. Technology allowed for self-tracking, which supported internal accountability. However, tracking by another person (personal touch) was needed for external accountability. Resources and environment underpinned the relationship among the themes of tracking, technology versus personal touch, accountability, motivation, and habit formation. CONCLUSIONS:Future research is needed to identify the best ways to harness this dynamic process in promoting and sustaining physical activity among inactive women. Digital technology is evolving at an exponential rate and provides new opportunities to transform research into new approaches to promote physical activity. TRIAL REGISTRATION:ClinicalTrials.gov NCT01280812; https://clinicaltrials.gov/ct2/show/NCT01280812. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID):RR2-10.1186/1471-2485-11-933.