I wish I could see Your subject face. There is not much to catch the attention on her back, except maybe the sport bra. It is hard to guess if this girl is looking at the other woman in the photo or not. There is some tension in Your shot I like it but it could be much better for my taste.
To Mirek: this is 1 picture from a serie, be patient then and perhaps will you get more in the next days... (but I'm afraid that you could be more deceived yet because I prefer the questions than the answers !) Cheers ! mc