Whatever you do, design it where you and your friends are NOT the targeted user group. As a potential employer, the portfolios that stand out are the ones where projects are not for some college kid.
If you are going to bite off something as large as performance/training/recovery/, please have a portion of your project dedicated to user evaluation of your ideas. And not having them look at pictures. Pictures can only get you “If it works, I like it.” Get user evaluation of how it actually works, get to prototypes quickly. Performance/training/recovery requires physical use.