We've been on several cruises, med, Asia, Caribbean, Scandinavia and Russia. You can get plenty of exercise from swimming pools, running tracks around the ship, ice rink, gym, climbing walls etc. Also go ashore most days for sightseeing, beaches, boat trips, sea swimming.
Food is fantastic with huge self-service restaurants, snack bars, or formal dining if you prefer.
Doctors nurses security all there for you and room attendants are excellent. Also a helipad to airlift serious cases to hospital and fly in cabaret entertainment stars.
Would not like to live on a cruise ship but love it for a holiday.
We went wit PO and Royal Caribbean. Definitely like marmite love it or hate it.