Jake Gyllenhaal transformed his body for the movie "Prince of Persia," spending so many hours at the gym that he says he became addicted to working out, eventually injuring himself.
Reality TV star Heidi Montag recently said she goes to the gym 14 hours a day.
Gyllenhaal and Montag are high profile examples of extreme exercisers – people who work out several hours a day to keep themselves fit.
Brooke Mora became an extreme exerciser after a going through a bad break-up.
Woman Works Out...Full Story