Looks good. You should think about adding Facebook Connect for registrations... especially with how much a lot of people like to announce how motivated they are to look after their health, and after all, "it's a good thing that you told everyone you went to the Gym, otherwise that session would have been totally pointless".

You should also make it clearly what your business model/pricing/fees/plans/what to expect once you sign up. This information is really difficult to discover without subscription.