Scree Running
There's nothing so sublime as when it goes right and you crunch down, pace after pace like seven-league boots or Hermes' winged sandals.
And nothing so grindingly smashingly bouncingly painful if it goes wrong.
It takes a LONG time to stop, and scree is a WEE bitsy jagged...
maybe six legs (wheels) would help, or maybe you just trip more easily?
(personally, I prefer snow-running. It hurts less!)