Raustyk has had both cruciates repaired on both of her back legs and they still bother her to this day. She's so enthusiastic that she still tries to jump & run etc... Of course if she gets away with it she's pretty sore for a little while afterwards though.
Nanook on the other hand, well he's a little smarter. When his arthritis first started to bother him he would limit his activity on his own. He knew what he could & couldn't do.

I know it's not HD but it's kind of similiar as both will affect how the dog can perform.

It's not that they won't jump or run it's that if they do it could cause more harm & pain is all. Some dogs are just better at managing what their bodies can handle or not. Of course adrenaline plays a roll too, if something entices them enough they may very well try to do somwthing that they normally wouldn't do otherwise.