I like that the design is very simplistic and easy to navigate. I think all apps should have those qualities.
The logo is confusing to me. I can't quite tell what the white thing is in the box. Is that supposed to me a mouth and the box is a face? Some sort of work-out equipment? I can't tell. I do like the font choice, though, and I like that you made part of the logo a box that way it will be easy to use for the icon on smart phones.
I really like the color scheme, but I do feel like there could be just a little more variation in it, specifically in the green buttons on a green background. Perhaps using some white or a more toned down color could be interesting to off-set the green.
I really enjoy the way you laid out the images so that they are clean and easy to view, and you can tell what the app is. It's also very pleasing to the eye. I also enjoy how you put the color scheme at the bottom.