Development of Artefact Removal and Physical Activity Algorithm for Continuous Activity Monitoring by Heart Rate Monitors in Cardiac Patients

This clinical trial will collect heart rate (HR) data with the Fitbit Inspire 2 fitness tracker and Polar H10 chest strap with the aim of: * Goal 1. Optimising and validating our artefact removal procedure. * Goal 2. Developing a physical activity (PA) algorithm to follow and quantify day-to-day PA based on HR measurements. A pilot study will be conducted with a total of 46 cardiac patients (group 1), 46 coached sporters with 12-week training schedule (group 2) and 46 sporters without 12-week training schedule (group 3). The three groups all engage in controlled activities. The participants' HR will be monitored continuously for an average period of 13 weeks using 2 HR monitors, i.e. the Fitbit Inspire 2 fitness tracker and the Polar H10 chest strap. They will wear the Fitbit device continuously for the whole monitoring period, while they will wear the Polar chest strap continuously for the first 24 hours and after that only during exercise. To determine participants' exercise capacity (e.g. VO2max), cardiopulmonary exercise tests (CPETS) will be carried out. For group 1, 3 CPETS will take place during the CR programme: at the start, in the middle and at the end. For group 2 and group 3, 2 CPETS will be carried out at the start and the end of the study. The monitoring period with Fitbit and Polar will end at the last CPET. All participants will record their daily efforts in an activity diary during the first week of study. Moreover, two questionnaires will be conducted at the end of the study to evaluates usability and experiences with the HR monitors.