JULIET DUFFUS, CNN CORRESPONDENT (voice-over): Looking for a challenging total body workout? It's time to get on the ball. Once used by physical therapists as part of rehabilitation regimens, exercise balls have moved from clinics into gyms. Dubbed resistor balls, these inflatable wonders can provide a well rounded fitness program for people of all ages, incorporating balance, flexibility and strength training.</s>UNIDENTIFIED FEMALE: It's used as a kind of an alternative to doing the same crunches on the floor or the same old squats, the same old stretches. It's just a new way to do it and it also, it's a lot harder of a workout because you're having to use, you know, stabilizing muscles. You're having to concentrate on your posture. You're having to really concentrate on what you're doing rather than just crunching off the floor.</s>DUFFUS: Exercise balls come in a variety of sizes so finding one that fits your body is a good start. Then begin by focusing on balance.</s>UNIDENTIFIED FEMALE: Try to lift up that right leg and hold it right there. Nice. Try to keep those abs and tighten that back straight.</s>DUFFUS: When you're ready to roll, move into a crunch to work your abdominal muscles. Try a pushup guaranteed to make you sweat and work troubled areas like the glutes by forming a bridge on the ball. Like any fitness program, consult your doctor before embarking and start and finish with a good stretch. So get on the ball and roll your way to total fitness. For "Feeling Fit," I'm Juliet Duffus.
Feeling Fit: Rolling Your Way to a Better Body