Sorry, not today

Ok so this week on my Medical ward saw another rather skinny turnout at my super awesome exercise class. I am not sure how to get an improved turnout. I know the pt. is ultimately responsible for their own choices and I do my best to educate them on the benefits of this group activity but still so many decline or come up with elaborate excuses. Am I not approaching it correctly?
I generally walk in and say that they have been chosen to attend because it is important for improving/ maintaining their health. Then let them decide. My supervisor, however, has the ability to turn "no" into "sure I suppose". Makes me crazy.
The one cool thing I suppose is I have a pt. who is consistently quite difficult to persuade but usually does, begrudgingly, head on down to the gym with me each day. Did I mention that he has amnesia? Yes indeed he does and thusly, not only does he not recall who I am each day but I get to practice changing my approach subtly each visit!! Perfect for me- although a doubt he sees it that way.
Anyway it is all a wonderful challenge I suppose and I will continue to accumulate successful strategies to gain compliance. However if anyone has some some insight into this skill. pass it along. Cheers,