Hi,
The forum has caught the reality nicely. Some platforms/vessels have good facilities, others have nothing.
On those with gyms, no problem, with those with nothing, if you are lucky you will have a helideck, otherwise a skipping rope, basic bodey-weight exercises and some piping on the deckhead for pull-ups will do. If you are into training, you will make a plan, if you are a body-builder or similar, you may want to cross your fingers you land up on something with a decent weight room and other goodies.
Good luck with the induction.
Rover22