Whats the benefit of setting a treadmill to a very steep incline? At my gym, the treadmills go up to a max of 15% incline. The other day I did some intervals where I would start off jogging on a flat surface and then increase the incline to between 10-15% incline and of course lowered my speed a little. I found myself eventually slowing down to a crawl and being completely exhausted, which really pushed me hard. Is this something that would help my fitness for tennis? What exactly does this do for you?