A micro randomised trial (MRT) to test the effects of app-based motivational messages on physical activity and heart rate.

INTERVENTION: Behavioural: Uniform random message delivery. In this arm, the categories and timings of messages will be delivered to participants using a random schedule. The study app will be available on the Apple App Store and on the Google Play Store. A member of the research team will assist participants to download the app, create a profile, and give a brief demonstration of the various functionalities of the app. The app will have a help section where participants can find detailed written instructions and a brief video tour of the app. An example of the physical activity notification that will be sent: "Going for a walk can improve your mood and clear your mind." Specific exercises will not be specified via messages for this study (MIRTH) because it is up to the participant to decide on the physical activity type, duration, and intensity. Message delivery will be monitored by accessing app analytics to monitor delivery of app notifications to determine whether messages are delivered to participants. Physical activity can be tracked via Fitbit devices, which our participants will wear 24/7 during the intervention period which will be 90 continuous days at time points 4‐6 and 10‐12 months. Baseline data will be collected for a full one month prior to initiating the intervention for the initial 4‐6 months, and at month 9 (natural baseline) for the 10‐12m study period. Participants will receive a personalised home program based on the guidelines of the American College of Cardiology Foundation / American Heart Association to treat individuals with stable ischemic heart disease. The principles we recommend are: 1) Do moderate‐intensity aerobic exercise for at least 5 days, preferably 7 days a week. Moderate‐intensity aerobic exercise is defined as ae CONDITION: Cardiovascular ‐ Coronary heart disease Sedentary lifestyle;Autonomic dysfunction; ; Sedentary lifestyle ; Autonomic dysfunction PRIMARY OUTCOME: Change in the number of steps walked within 180 minutes after messages are sent at each decision‐making time point as determined from Fitbit device data.[Cumulative data will be assessed at the end of months 6 and 12 of the intervention.] Change in heart rate within the next 180 minutes after intervention as determined from Fitbit device data.[Cumulative data will be assessed at the end of months 6 and 12 of the intervention.] Change in the duration of time spent exercising (physical activity) within 180 minutes of receiving the message as determined from Fitbit device data.[Cumulative data will be assessed at the end of months 6 and 12 of the intervention.] SECONDARY OUTCOME: Compliance (Time Frame: 180‐minute window while message is available) as determined from Fitbit device data.[Cumulative data will be assessed at the end of months 6 and 12 of the intervention.] Heart rate variability (HRV) using 3‐lead ECG. [Cumulative data will be assessed at the end of months 6 and 12 of the intervention.] Time of day when the majority of exercise compliance occurs (e.g. morning, midday, or evening) as determined from Fitbit device data.[Cumulative data will be assessed at the end of months 6 and 12 of the intervention.] INCLUSION CRITERIA: 1. Intervention group participants from the LIVEPLUS study (ANZCTR registration: ACTRN12620001151921). 2. Adults who can competently use a smartphone (running iOS or Android) 3. Presence of Low attenuation plaque on Coronary Computed Tomography Angiography 4. 18‐80 years of age 5. BMI greater than or equal to 22.0 kg/m2 6. Have no contraindications for the LIVEPLUS study 7. Able to give full informed consent