Where are you staying? The Marinha Dourada resort has a gym of sorts, a few machines, not exactly hi-tec ( or it wasn't 2 years ago!), but I intend to do a few circuits of the lakes around the MD this year when we go in 2 weeks time.
Sorry don't know of any public gyms, maybe in Calangute

There is a good gym not far from Arpora - on the main road to Calangute behind the Spitfire pub. Forgotten it's name but will have a look when I go out.
Very well equipped, AC, showers etc. Will let you know.

Were staying at the Marinha Dourada but I looked at their equipment last year and I dont think our insurance would cover you on it The gym behind the spitfire seems ok