We have never paid to participate in the organized fitness classes and I think the cruise lines are missing an opportunity here.  I would be interested in trying Pilates, yoga, spinning, etc, but I don’t want to pay for something I may end up hating.  (I would never have paid to try escargot, but after having and enjoying it on a cruise I will now purchase it in a restaurant.)  If there were complimentary “introductory” classes I may end up paying for more later in the cruise or on future cruises.