"Because your muscles are actually doing a lot of work, keeping you balanced and moving in rhythm," Karla said, a tad smugly.

Hey, she'd grown up riding a lot. Sure, she hadn't ridden for days on end...ever...but she was doing pretty well with the soreness, relatively speaking.

...She had another reason she might not be as tuckered out as everyone else, but that was a joke to be shared not where strangers could hear her. Heh.