As far as I know there is nothing much more you can do. You just may have to play for a while and try back at a later time.
I have also updated info on the gym glitch
8. Can’t work out or The Gym glitch.
You went to the gym to work off that extra cluckin bell you had on your date, but you get the message “you’ve reached your limit for the day, come back tomorrow.” But you have not worked out for days, WTF.
Cause: Seems random at most times, but does seem to occur more after finishing the story missions. One known cause is saving away hunger. If you save the game instead of eating when the game tell you CJ is hungry you will get this glitch. It’s not the only why thou.
Fix: There are a few. The first thing you can do is eat a bunch of meals, they can be salad meals. Eat 11 meals then try to work out. You may have to save after eating for it to work. You can also raise one out your stats, I know raising the gambling, and the lung capacity stats have worked. If nether of these work try to play for a long time with out saving the game, 5-7 in game days. I have always “played” while trying this, I don’t know if just letting CJ stand there will have the same affect. The final why is to change every thing about CJs appearance, hair, tattoos, clothing, build (gain fat). If none of these work you may have to deal with not being able to work out. Most of the time the glitch will right it self sooner or later (could be much later). This is not crippling, if you keep a little bit of fat (5-10%) on CJ he will not lose muscle.
I have also found that Secrets Guide by The Duff Man on gamefaqs.com has some good info about this glitch.
click the link and then scroll down to the botom of the page to find the guide.