I was on the Horizon in February and 2-3 aerobics classes were scheduled every day. The two different instructors I had were excellent. There were two problems that the hard-core exercise people (like me) faced. 1) Lack of a dedicated aerobics area - it is a small ship, after all - so classes were held on the show stage or in one of the lounges. 2) Not enough exercise mats for the class. The first abs class that I attended had 18 people and the instructor said that they only had 12 mats because "we've never had more than 10-12 people show up". I don't know if that was true or they just lack storage space for more mats but the class just made the best of it by sharing the mats. A great cruise, by the way.