when i do sprints i mark off roughly 60 yards and i just shuttle run... i do sets of 10 or 15... run a sprint, turn my ass around, walk back, get right back on the line and do another and another and another... honestly i get a shitload out of it... generally, if im at a track, i do this then i go right to the stairs and get moving up and down sets of 10 but serious flights... sprint to the top, slowly come down etc... these are both HIGHLY effective...