the way I see it is this: your user audience are people who want to be more aware of their fitness so your goal should be to partner up with businesses in your niche to attract customers. I'm thinking ebooks, sportswear & stuff, cooking books and so forth. you can also do affiliate contracts.

also, you should give great priority into building a proper email list and, on the other hand, find the right email marketing strategy to attract more users and keep existing ones. in your case, the tone should be very personal, look around how other fitness companies approach this.

the experience of the app should feel progressive on more than one level, so not only a static collecting of points. give them the opportunity to multiply their collect if they skip a day for example. it's a math thing.

and last but not least, and this is the most important for the marketing of you product: you have to find your way to fully understand the user/customer, as much as you possibly can: the less it sounds like you want to sell them something, but instead really help them with their problems in a creative and motivating manner, you are golden!

I'm not an expert, but this is my point of view.
good luck with it.