I've used the curve before. I actually thought that it felt harder doing sprints on the curve as opposed to doing sprints outside on a track. I did find it awkward at first (mainly starting), but I soon got the hang of it and I really felt an intense "pump" in my hamstring and glutes. Overall, I really liked it... mainly because it really goes well with the way I run/sprint as opposed to other treadmills and even the treadsled (I felt like the treadsled is too much "push" and you really have to lean in and I run more upright and with more "pull"). I hope this helps.