If you are serious about turning this into a real business, there are some things you absolutely have to do:
1. "Dashboard", "routines" and "workout" show me the exact same page
2. Video is cool, but I'm not going to watch it because it's so linear. I just want one particular feature, and I don't have the time to sit and watch 10 minutes or whatever of video to find out if you have that feature. (I don't know how long the video really is, because it's not written till I push play, which I don't want to do)
3. Content is king. If you want to make a site, you need to struggle for every single user! Getting linked from techcrunch is an utter waste of time, because they are not your target user. Your target users searched google 40.000 times today for your site. If you had 5.000 pages of content, you'd get a percentage of those searchers. And easy way to start is by making your routines public
4. All you're interested in is one user. You need to continuously examine the flow of that one user - when he hit your page right up until when he signed up. Do you know EXACTLY where he clicked and what he was looking for? If you don't, it's like having a car factory, and you're not sure what steps the assembly line goes through to product a car
5. I have an iPhone, and your app actually sounds interesting to me. But there are no screenshots and no description of what this iphone app could do. So I'm going to close your site and forget about it instantly
6. Go to delicious.com/popular/fitness for inspiration
7. Categorize your users. I don't know the natural categories for fitness, but maybe something like "people who want to lose weight", "people who want to body build and are doing it regularly", "skinny guys who want become somewhat muscular". For each category, look at your site again. Does it seem attractive? Are this category of interest to you? Then examine each category - which is the most profitable?
8. Remember that any idea you have is just an idea, and you don't know if it works. If you implement it and it works, this does not mean it was right. For example, let's say you have the idea that green may be the best color to encourage people to sign up. You change the color to green, and you have 5% more sign-ups. You'll sit back and feel satisfied that your idea worked. Big mistake, because red may have caused 50% more sign-ups. So when you have an idea or hunch, make sure you test the alternatives, even if it seems to you that they won't work.
That's all I got for now. Good luck!