Gurezaemon:geoffwnz: Gravity. Particularly when applied rapidly. Or at least, the sudden stop after a sudden attack of gravity while snowboarding.
Turns out ice plus catching a heel edge hurts a lot.Usually on the last run of the day, where you've thought, "I'm getting tired, but I'll be all right..."
For me it was a front edge combined with ice = broken rib.
Certainly became the last run of the day, though I was only heading back for lunch initially.
Variable conditions meant some trails were crisp, some were softening, and that one green return trail that was shiny ice...