I think this depends on the crew on the boat. I have cruised ACL twice, and things I thought would repeat from first experience to my second varied. An example is that the first cruise I was on had visual arts classes as part of the daily itinerary and the second cruise did not. First cruise had a duo team doing lectures and performing nightly entertainment, and my second cruise had a solo historian and a solo entertainer. First boat had freely available beers and wine in a self-serve station, and the second boat only had alcohol available during the evening or “by request” any other time. Haven’t cruised the Jazz myself, so I can’t answer specifically but hope this sparks someone else to jump in. I’m guessing that if your Cruise Director or other administrator/officer is into fitness then they’ll probably offer classes. The Cruise Directors, Tour Managers and Assistant GMs seem to be the ones who “play to their strengths” to bring excitement to the guests with their individual talents like playing an instrument, doing comedy, history lessons, and maybe even fitness.
The good thing to know is that ACL never charges for any onboard services to my knowledge, so if they do wind up having group classes it would be complimentary.