Short Answer: Yes.
Long Answer: You should have access to all the fitness facilities aboard your ship in the same manner you would on a traditional cruise.
Most ships feature at least a jogging track and workout room with treadmills, machines, and dumbbells.
Personally, I haven’t seen a great deal of free weights available, but if you’re looking to run, do some curls (because of course you’re going to do some curls), or anything else, the onboard gym is at your disposal.
Also, in my experience, it’s not really packed. I thought I would see more people working out given the nature of this party, but that wasn’t the case. We’re all here to party, after all, not workout like we do the other 51 weeks out of the year!