  Gamification represents an effective way to incentivize user behavior across
a number of computing applications. However, despite the fact that physical
activity is essential for a healthy lifestyle, surprisingly little is known
about how gamification and in particular competitions shape human physical
activity. Here we study how competitions affect physical activity. We focus on
walking challenges in a mobile activity tracking application where multiple
users compete over who takes the most steps over a predefined number of days.
We synthesize our findings in a series of game and app design implications. In
particular, we analyze nearly 2,500 physical activity competitions over a
period of one year capturing more than 800,000 person days of activity
tracking. We observe that during walking competitions, the average user
increases physical activity by 23%. Furthermore, there are large increases in
activity for both men and women across all ages, and weight status, and even
for users that were previously fairly inactive. We also find that the
composition of participants greatly affects the dynamics of the game. In
particular, if highly unequal participants get matched to each other, then
competition suffers and the overall effect on the physical activity drops
significantly. Furthermore, competitions with an equal mix of both men and
women are more effective in increasing the level of activities. We leverage
these insights to develop a statistical model to predict whether or not a
competition will be particularly engaging with significant accuracy. Our models
can serve as a guideline to help design more engaging competitions that lead to
most beneficial behavioral changes.
