Wow, I can see what you envision for your app and I must say its a great concept, different from most fitness apps.

I don't think any hospitals will be providing any patients information (privacy) also its the wrong target market

- you want to target the Fitness Trainers - Similar to a social network for fitness trainers - that their clients can follow and say up to date with.

Firstly Post invites to beta testers to

Google+ and Facebook Fitness Communities

Tailor it to the fitness trainers as a way to show their photos, build clients, and book and organize their appointments.

Think about it like ths - Every personal trainer you get on the app - the more they will have their clients download and use the application. This will be the key to success. If you want to use a clever trick to build up users - provide PRO features in the app that the trainer can only unlock when they have 20+ Users sign up to their account. This will heavily encourage them to get your app more users