"Over there, look," trainer Julieanna McGuire says, pointing discreetly toward a young woman stretching her back over a large rubber exercise ball. "I used to try to correct them, but now it would be a full-time job."
Anyone who has been to a gym in the last decade has seen people working out with inflatable exercise balls, sometimes called Swiss, stability or yoga balls. But, as McGuire points out, few have seen them used properly.
Strengthening and developing the body's core -- primarily the abdominal and back muscles -- is the reason for working with an exercise ball and an outgrowth of the Pilates philosophy. The ball's instability means you must continually work your core muscles to balance yourself on it or against it. Rather than targeting the extremities and large muscles, as most gym gear does, the ball forces you to engage trunk muscles, even while working the arms and legs.
"Balance and posture are critical to every activity, from dancing to just walking," McGuire says. But they're "so often neglected, mostly by guys, who usually come to the gym to work their arms and legs."
McGuire incorporates ball exercises into every client's training session at the Washington Sports Club in Chevy Chase, Md. Novices can do basic exercises, such as push-ups with hands on the floor and the ball elevating the thighs. Doing the exercise this way increases gravitational resistance and, more significant, activates abdominal muscles needed to maintain the position. The closer to your ankles you move the ball, the harder the exercise gets.
Ball sit-ups, another basic exercise, also take balance and constant core adjustments while engaging the abdominals more directly. (Keep that ball fully inflated. A squishy ball decreases balance issues and makes such exercises less difficult.)
Intermediate-level exercises include squeezing and lifting the ball with your legs while lying flat on your back. Once the ball is overhead, rotate it back and forth 90 degrees from your core. Return to start. Repeat.
More-advanced exercises incorporate dumbbell repetitions while seated on the ball; maintaining coordination and balance makes resistance training even more challenging. The Mayo Clinic presents a good slide show of some stability ball exercises at www.mayoclinic.com/health/core-strength/SM00046.
Oh, and what's the problem with arching your back over the ball, as so many people do? You think you're stretching the muscles in the center of your back, but you're actually contracting them. Better to lengthen the back muscles, McGuire says, by simply touching your toes.
Exercise balls aren't just for the gym. Some cost as little as $10. They come in a variety of sizes, 55 centimeters to 75 centimeters in diameter; 65 centimeters is usually a good fit if your height is 5-foot-8 to 6-foot-3. You've got the right size if you can sit on the ball with your feet flat on the floor and knees bent at 90 degrees.