Under threat of being gelded, this pony ran on the treadmill in full tack (which is bad enough for any length of time, believe me). However, running in hoof boots can be so exhausting (and painful if you're out of practice walking like a horse or on pointe).
Indeed, this pony came off the treadmill out of breath, sweating profusely, and with his toes (and nipples, damn nipple clamps) on fire! Nevertheless, it was a good time and these scenes, while often exhausting, leave me reliving them in my mind for a long time afterwards.
Now, if only we could do a public treadmill scene, that would be hot!