BACKGROUND: The ecological momentary intervention (EMI) is one of the most promising digital-primarily mobile-interventions to enhance physical activity (PA) and other health behaviors. It is a combination of ecological momentary assessment (EMA), in which participants are prompted to indicate their momentary states and ongoing behaviors in daily life, and the just-in-time delivery of interventions tailored to the EMA responses. The EMI has typically been implemented in message-based interventions (eg, activity recommendations tailored to users' physical locations), but its efficacy and feasibility have not been sufficiently established because of the variability in design and implementation.
OBJECTIVE: This pilot, two-arm, parallel-group randomized controlled trial aimed to be an exemplar of EMI for improving PA and establishing efficacy and feasibility among adults without a habit of PA.
METHODS: A total of 40 participants (23 women; mean age 45.40, SD 10.50 years) were recruited from among community dwellers in northeast Japan and randomly allocated to the EMI or control group. Each participant wore an activity tracker to monitor their daily step count and heart rate (HR) for 4 weeks (fully automated). Simultaneously, they responded to EMA questions about the current weather, location, and social context 3 times during the daytime and an additional evening question about motivations for PA each day. Only the EMI group received messages tailored to their responses to EMA, recommending more active alternative behaviors suited to EMA-reported contexts.
RESULTS: Participants wore a Fitbit device for 90.3% (21.66/24 hours per day) of the study period (mean 90.3, SD 10.0), and no dropouts were observed. The EMI group showed no significant improvement in the self-reported amount of PA (P=.44), step count (P=.24), or motivation for PA (from P=.11 to P=.91) compared with the control group. However, the EMI group showed a significantly larger increase in the minutes of 40% HR reserve, a measure of moderate or high intensity of PA (mean 16.03, 95% CI 3.76-28.29; Cohen d=0.20-0.41; P=.02 for the follow-up weeks). The intervention was rated as marginally useful and satisfactory, and approximately half of the participants expressed a willingness to continue the intervention. The timing of the EMA prompting was considered inappropriate.
CONCLUSIONS: These findings suggest that the EMI with messages tailored to EMA-reported contexts was not effective in increasing the amount or motivation for PA but may increase the intensity as assessed by the HR. The intervention aimed to help individuals implement small but slightly more active behaviors in their daily routine, which may not accompany prominent body movements but may be reflected in the increased HR. Marginal feasibility indicates that the intervention has sufficient scope for improvement, particularly in terms of prompt timing.
