You may be able to narrow your project to a specific problem within the fitness application market that can be addressed with one of the ACM domains. On the other hand, I like how the app would have the option for the user to send their workout report to their doctors or therapists, so the professionals would generate a better treatment plan for their patients.

The question is, What would be the problem statement for this project? regarding the User-interface and the Report from users to the doctor?