Thinking Outside the Ball

When we refer to outsize inflatable holiday amusements, we're not talking about that fake eight-foot snow dome on your neighbor's lawn. We're talking (again) about stability balls, those colorful orbs said to help you develop functional strength and balance. Since they are cheap and inherently fun -- balloons for fitness-seekers -- they make good gifts to give and to get. With several new types on the market (of which more below), we thought we'd return to the timeless question: What are they for, anyhow?

Doing many exercises, including crunches, chest presses and bridges, on a stability ball forces you to employ ample muscle fiber for both force and balance, says David Behm, a professor in the School of Human Kinetics and Recreation at Memorial University of Newfoundland. Exercising on a stable surface -- floor, weight bench, church pew on Christmas Eve -- recruits muscle almost exclusively for force.

"When you are unstable, you'll use 40 to 50 percent of the muscle fibers to lift the weight and the rest to stabilize yourself," Behm says.

This has the immense benefit of helping you develop a mix of strength, balance and flexibility to lower your risk of injury while you meet the physical demands of everyday life and athletic pursuits.

In a study of six men and five women age 20 to 45 published in February's Journal of Strength & Conditioning Research, Behm found that doing trunk (core) exercises on a stability ball caused greater activation of the lower abdominals than doing the same exercises while stable. The same study showed that chest presses done on a ball recruited far more trunk-stabilizing muscles than did presses done on a bench. No such effect was shown for shoulder presses.

"The most effective means for trunk strengthening should involve back or abdominal exercises with unstable bases," Behm wrote in the study. Other research has found improved athletic performance in those who do balance exercises rather than pure strength training.

A notable caveat: If you are seeking to bulk up -- and only bulk up -- stick to the weight bench. Muscle fibers that are working to stabilize you will not participate in the forceful lifting that creates more muscle mass.

Bored with your stability ball or need a last-minute gift? A company called PowerSystems ( http://www.power-systems.com ) offers some spinoffs worth a look.

The VersaCore Trainer ($100) adds a stable base beneath a ball, helping beginners manage. The VersaBall FX ($170) adds a seat, metal frame and exercise bands to create a stability-ball exercise station. The VersaRoller ($40) is a plastic kidney bean that keeps you closer to the ground and permits different functional exercises. Local and online fitness retailers have similar products, including one called Spri ($40 to $50), a ball with stubby legs that look a bit like udders.

Take care with sizing. Folks who are under 5 feet 7 inches tall will likely do best with a 55-centimeter ball. Up to six feet, 65 centimeters. Over six feet, 75 centimeters. When sitting on a well-fitted ball, your thighs will be parallel to the floor and your feet on the ground.

That's all for 2005, folks. (The Health section won't publish next week.) Stay balanced, fit and safe. We'll see you Jan. 3 to kick off a new year, firmly resolved to . . . oh, we'll figure out something by then.

-- John Briley