Can workout apps actually motivate users to sustain an exercise routine? If so, what are the key characteristics of these apps that engage long-term users? We conducted a content analysis to find out. Guided by the Motivational Technology Model and Self-Determination Theory, we explored the relationship between technological affordances of BodySpace, a highly ranked body building and weightlifting app, and behavioral outcomes (number of workouts tracked, weight lifted, and cardio hours) and goal attainment rate (percentage of body fat and weight goal achieved). A total of 682 profiles were used for analysis, revealing that the use of features of the app that elicit relatedness, autonomy, and competence predicted exercise outcomes. However, these relationships were moderated by gender, consistent with prior research on the differential workout motivations between males and females.