Have you seen the gym/spa at Swept Away?? I think you can go there for $25pp...You can spend a half day there,spin class,pool,weights,bar,tennis etc.....
ROOMS on the BEACH has a small but new looking gym - has cardio and a few free wts. not sure if you can use it or it they have a fee. It was empty most of the time I was there and is air conditioned
I do walks on the beach,from Bloody Bay to the Boat Bar,Red Stripe there then back.However if you want to spend 4 hours at the Swept Away,work out,swim,get smoothies,beers,hot tub??? Its like an excursion for $25.