Darcy Ummels

146 | Chapter 7 available activity trackers that were on the market in May 2015, a total of 72 trackers were found to be eligible. To ensure that the scope of different system requirements was covered, trackers were randomly selected based on the following criteria: variety of tracker location, variety of activity tracker types (e.g. accelerometer) and variety of tracked variables (e.g. steps and heart rate). By randomly selecting the activity trackers based on the above criteria, a representative sample of the range of activity trackers in 2015/2016 was used to test validity and feasibility. Since the beginning of this dissertation in 2016, the commercial market of activity trackers has exploded, with more brands, more diverse activity trackers, and trackers integrated into smartwatches and smartphones. The commercial market of activity trackers mainly targets healthy adults, athletes and people who exercise regularly. With this focus, more new variables and features were added to current activity trackers (e.g. guiding breathing sessions, playing music, enabling paying with one’s activity tracker). In addition, some activity trackers that were used in this dissertation are no longer available. Therefore, one could argue that the specific results of phase one have become outdated. However, these results are still applicable because the underlying algorithms of most activity trackers have not changed or were optimised for an active population instead of (older) adults with a chronic disease or older adults with or without chronic diseases. The results reported in chapter four confirmed this statement when three more recent activity trackers were validated together with the MISS Activity. The latter proved to be more valid than the three recent activity trackers in older adults with or without chronic diseases during activities of daily living. In contrast to these algorithms, the user interfaces of activity trackers have changed in the past five years. The first activity trackers were fairly simple to use, but adding more features to them and embedding them into smartwatches and smartphones made them more complex to use, especially for older adults. However, incorporating them into smartphones could also be useful, since it might be more appealing to start measuring physical activity with a smartphone one already owns than to buy a new activity tracker. It is to be expected that the experiences of (older) adults with chronic diseases and older adults with current, commercially available activity trackers will most likely be the same. The target population In this dissertation, both (older) adults with a chronic disease and older adults with or without chronic diseases participated in different phases. Within the performed studies, algorithms were validated in both target populations. There is a strong overlap between older adults and (older) adults with a chronic disease. In general, both groups have