Stefan Elbers

178 Chapter 7 Mobile Health The emergence ofmobile health (mHealth) provides newopportunities to support behaviour regulation to maintain or enhance the long-term treatment effect of IMPT progammes. Despite substantial variations concerning study quality, interventions, and outcomes, mHealth apps are generally regarded as a promising strategy to facilitate adherence to treatment principles or to increase self-management skills (e.g. Anglada-Martinez et al., 2015; Rathbone & Prescott, 2017). A specific advantage is that an app can include multiple interacting behaviour regulation strategies within its digital environment (e.g., automatically linking personalized goal setting regarding physical activity to accelerometer output). Moreover, mHealth strategies can integrate other smartphone functionalities such as digital calendars, instant messaging services, or a camera, thereby offering personalized behaviour regulation strategies that support the transfer of treatment insights into each patient’s personal environment. Despite the potential and current popularity of mHealth apps, the effectiveness on health-related outcome measures varies greatly (Byambasuren et al., 2018). Factors such as engagement—defined as the extent of app use as well as the corresponding subjective experience (Perski et al., 2018)—and usability—defined as the relative ease with which users can use an app to achieve a particular goal (Coursaris & Kim, 2011; Zapata et al., 2015)—may account for this variability (Byambasuren et al., 2018; Zapata et al., 2015). For example, patients that use an app to change their health behaviours may use the app in a different way than intended or stop using the app after several days, which prevents facilitating the intended behaviour change (Perski et al., 2018). Therefore, evaluations concerning the effectiveness and clinical importance of mHealth apps on health outcomes should take evaluations on user engagement and perceived usability into account (Pham et al., 2019; Zapata et al., 2015). Previous Studies In 2015, we initiated the SOLACE research project to develop strategies to prevent relapse after IMPT progammes. Because there was little research available on this topic (Morley, 2008; Turk&Rudy, 1991), we started with an 18-month co-design project, in which patients, health care providers, researchers, and designers shared their expertise and collaborated to develop ideas, concepts, and strategies to prevent relapse after successful treatment. This resulted in a prototype paper workbook that contained the two most promising strategies: a valued-based goal-setting procedure, and a method for storing and facilitating retrieval of meaningful treatment experiences. Subsequently, we performed a feasibility study in which the prototype workbook was tested at two different IMPT progammes for 6 months. Overall, patients and health care providers were willing and able to use the workbook and