As someone who got very good at DDR at a young age, and is now older, it's clear that if you do any exercise which challenges your balance when you're young, your balance will be better when you're old. I haven't practiced slackline or DDR in decades and I don't really exercise now, but I can still walk across a log found during a hike like it's nothing. Strength may come and go, but balance is clearly some kind of long-term muscle memory.