Dear God, that looks terrifying (and fun!). I think he should maybe have a helmet on or something. I think if the person in the background weren't there I would like this a bit more, though I'm sur you had no control over that at the time! Fun shot.
I am not voting on this image but if I did I would more than likely give it a 4 or lower.
Let me explain, I "personally" don't think you met the challenge's request to take an image of a "stock" photo of fitness. Your photo isn't bad or physically hard to do but I just don't think it's a "stock" or "fitness" style image.
The author has done very well here conveying a sense of freedom and joy. This could have gone two ways either focusing on the dogs or the way the image is presented. Either would have worked well and this is the best so far. A little awkward composition and a little faster shutter speed along with the excellant tracking that the author used would have made this perfect.