I've been meaning to post about this for awhile!
Muscle Beach has set up in Rio for 3 months - the "summer" - is free of charge, offers lots of classes! To use the facilities you do have to register and it is open to tourists as well, but what I don't know is whether or not it is still open to registration. Anyway there are a lot of outdoor "gyms" in Rio along the beach but this one is certainly the most state of the art I've seen, apparently there is also one in Barra.
To read more about Amil's Muscle Beach on Ipanema or Barra beaches, click here.