There was once a time when I actually got more running done on vacation but now it probably is just the opposite. "Sit back and relax" sounds more melodious.
I am happy to give up going to the gym while I am away - no regrets at all. Sometimes my "vacations" are for the purpose of going running; i.e., Oringen. I can foresee other situations where I would be happy to substitute long walks, such as during a visit to NYC - but then Central Park beckons.