Insider's Guide to Stability Balls

Stability Ball 101

A stability ball works your abs way more than regular crunches do. Plus, use it in place of a bench for strength moves and your core gets a workout -- you'll engage your deep obliques and lower-back muscles to stay in place, says Stephanie Dupuis-Morris, co-owner of Resist-A-Ball.

It's adaptable to every fitness level. For beginners, the ball provides support to make moves like push-ups easier. More advanced exercisers can add challenging balance positions to basic strength moves like bridges and lunges.

It helps banish back pain. Physical therapists love the ball because it strengthens the deep muscles of the spine. One recent study found that subjects who used the ball regularly improved muscular endurance (the number of consecutive reps you can do) by 57 percent in 10 weeks.

• Choose the right ball for your height -- 5': 45-cm ball; 5'1" to 5'7": 55-cm ball; 5'8" and up: 65-cm ball.
• Inflate the ball enough so that when you sit on it with your feet on the floor, your knees are even with or just above your hips.
• To make the exercises more difficult, add more air to the ball: The firmer it is, the greater the challenge.
• Stability balls start at $15.95, depending on size; hand and foot pumps are available from $7.95. For more information, go to resistaball.com.