Originally Posted by Pleasurepays

i've wondered about that in the past. most treadmills have a significant amount of bounce/flex to them. if you study human kinetics, its amazing the amount of forces your body can absorb, but its all done within the limits of very specific movements/ranges of motion etc etc etc. when you start to stray from those and start to introduce more awkward/less natural motions/movements, you can have serious problems.. for example, hurt your ankle, then you start running a little funny (even unnoticeable) ... your opposite knee starts to hurt.. then your shoulder etc. the balance of how your body deals with motion/force is very delicate. it wouldn't surprise me at all to see someone seeing issues from running on treadmills... especially those with significant amount of flex to them.. however, the odds are definitely on the treadmills side, given how many people are running on them each day without issue.