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The advancement of current technology allows developing lightweightunobtrusive devices, which detect human physical activity. However, there has always been a major issue, hindering the regular usage ofthese gadgets - many people find it difficult to fit them in theirdaily routine. In this thesis, we develop an application, which allows us to measure the influence of online social networks on people involved in physical activity programs. On the grounds of our literature research, we identify different motivational triggers that can be employed for the design of a social network application in the context of physical activity programs. Based on these findings, we design and implement the ActiveTeam application, using Facebook as underlying social network service. In the course of the document we propose several methods to evaluate the behaviour of ActiveTeam users. These methods areintended to help us analyze and improve the application once it ismade available to a large number of users.

This report describes the theoretical background and development of an application to share physical activity information, as well as the results of a four-week field study in which people shared physical activity information as measured by the Philips Activity Monitor. The existing web-service DirectLife was enhanced with an interface that visualizes similarities, activity levels and patterns between users. The application, developed by deploying user-centered design methods, displays several attributes of physical activity. During the field study two groups of seven participants carried the activity monitor and shared activity information; either visualized on a publicly shared or private display. Visualizing similarities in physical activity is expected to increase interpersonal awareness, communication and perceived closeness. From the perspective of self-determination theory (SDT), this should increase the fulfillment of the need to belong. Such a fulfillment is expected to increase intrinsic motivation for physical activity and engagement in using the activity monitor. The results show the promise of using similarity and enhancing connectedness for technology-based persuasion. In addition, several recommendations are made for future efforts aimed at increasing motivation for physical activity.

Prolonged sitting time is a potential health risk, not only for people with an inactive lifestyle, but also for those who do meet the recommended amount of physical activity. In this paper, we evaluate SitCoach, a mobile application to nudge people from their seats. SitCoach monitors physical activity and sedentary behavior to provide timely feedback by means of suggesting sitting breaks. A pilot experiment with a group of 8 users learned that the general awareness of the importance of sitting breaks is low. Combined with the belief that the ability to take sitting breaks is highly dependent on externalfactors, a strategy of proposing break reminders may not be the most successful for this target group. Future work should focus on creating awareness of the problem and providing insights into personal sitting behavior.

Prolonged sitting is a potential health risk, not only for people with an inactive lifestyle, but also for those who do meet the recommended amount of physical activity. In this paper, we present two waysto promote the reduction of sedentary behavior. First, we report onan experiment in which office workers (n = 40) received timely persuasive messages on their smartphones, advising them to take an active break whenever 30 minutes of almost uninterrupted computer activity was recorded. The messages resulted in a significant decrease in computer activity and a peak in physical activity, indicating that participants complied to the given advice and took short breaks upon receiving a message. Second, we developed SitCoach, a mobile application to nudge office workers from their seats. SitCoach monitors physical activity and sedentary behavior to provide timely feedback by means of suggested sitting breaks. The results of a user test showedthat the general awareness of the importance of sitting breaks is low. In addition, the ability to take sitting breaks was considered to be highly dependent on external factors. This suggests that raising awareness and increasing self-efficacy are important prerequisitesfor a successful intervention to reduce sedentary behavior.

We study the effects of digital photo sharing on social connectedness of people with special needs. We target people dealing with a transition in life that forced them to live away from their family and friends. Our study included four people with spinal-cord injury staying in a rehabilitation centre and eight elderly people staying in a nursing home. Each participant was provided with a web-enabled digital photo frame and their family members were provided with a camera phone. The results of our study show positive effects. For rehabilitants photo sharing simplified the way they could reconnect to their family. For the elderly people, photo sharing served as 'food for talk'.

This report describes the use of personalized persuasive messages toinflu-ence healthiness of menu choice. The susceptibility to persuasion scale (STPS) was used to assign participants to different strategies. We hypothe-sized that persuasive messages would have a positive effect on menu choices. A 10-day experiment was setup to evaluatethe effect of susceptibility, in which the users were exposed to persuasive messages about healthy eating. Each of the persuasive messages implemented a particular social influence strategy. In total, 324 participants made a daily menu choice out of three presented menusthat differed in health score, for ten days in a row. The analysisincludes multilevel (regression) models that were fitted to accountfor the interdependency of the data points. The experiment does notshow significant evidence for any of the hypotheses; personalized (tailored) messages did not lead to healthier menu selection than contra-tailored, random or no messages at all. Therefore, it is assumedthat food choices are affected more by other factors than the subtlepersuasive intervention that was used in this study. However, participants were also asked to estimate the health of each menu. A (negative) effect of persuasive message principles was found on the health estimation of the menus. We suggest that the decrease in health estimation is caused by an increase of the health ideal. Furthermore,the results are compared to related work in the field of personalized persuasive messages. In particular with a similar study that has investigated persuasive effects on the reduction of snacking, here researchers found opposite results. The results of this study will help in designing a persuasion engine that will be implemented in the smart kitchen scenario, which has the purpose to create context awareness and empowers people to eat healthy.