Oscar winner Charlize Theron has vowed to stay in shape - and has joined a gym for the first time ever. The 32-year-old star - a former model - insists she's never felt the need to pound the treadmill in her local gymnasium to stay slim, but is enjoying the social aspect of collective exercise. She says, "I'm not really comfortable with the gym. I prefer hiking and biking, although for the first time in my life this year I joined a gym and I go with my girls from the office because, God, I can't go on my own. "We go to classes like Long n' Lean and just stand there laughing."