Startup Idea : Community platform for heath clubs

I develop custom social networks and had this idea a while ago when visiting my gym. Why do none of then have custom social networks? Everyone has something in common at those places, and when you take a class it would be fun to contact one of the people there. Every class or activity could have its group and the member's profiles could be as complete, or as vague as they wanted - and of course you could control all communication. This would be a hybrid online / real life network that I think would be fun and would add value to the health club membership.