Essentially what rndmguy said, but I am going to add on. Can you swim? I imagine that it would be a fairly low intensity exercise, but still be enough to get you fit. Also, try squats while you are in the water to strength train. Aqua-aerobics are often prescribed to those who normally have issues like that.
Powerline!Max - A Goofy Movie (Otakon 2015, completed)
Possible Future Cosplays
Ippo (Hajime no Ippo)
Guts, Golden Age (Berserk)
Teen Goku (Dragonball/ Dragonball Z)
Steve Rogers civilian uniform (Captain America: First Avenger)
My Facebook cosplay group - Southern Maryland Cosplay
(Anyone can join)
Author of the "Getting Fit for Cosplay" Katsucon panel.