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

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 aerobic exercise at 64% to 76% of maximum heart rate (HRmax) (see Riebe et al. 2018) 2) Increased daily physical activity (e.g., work breaks, gardening, housework). 3) Do strength training at least two days a week. There is no specific training program for everyone, but these general principles are personalised based on baseline activity level and annual progress. Strength training is a form of physical activity that is designed to improve muscular fitness by exercising a muscle or a muscle group against external resistance, for example, body weight, free weights, dumbbells, etc. Body weight training videos of 11-minute duration will be made available. No external equipment will be required. Exercises range from step jacks, toe touching, wall push-ups, to high knee running, bicycle crunches, and high plank to low plank. The goal of all participants is to achieve at least 150 minutes of moderate intensity aerobic exercise per week. In addition to the training module, the team has also developed a series of circuit training videos for different intensities for a wide range of fitness and self-confidence levels that can be viewed at any time via the study app. The duration of the circuit training videos ranges from 11-33 minutes including a 5-minute warm up and a 5-minute cool down video. 1. Riebe D, Ehrman JK, Liguori G, Magal M. Chapter 6 General Principles of Exercise Prescription. In: ACSM’s Guidelines for Exercise Testing and Prescription. 10th Ed. Wolters Kluwer/Lippincott Williams & Wilkins, Philadelphia, PA: 2018, 143-179.