On half a ball, a full ab workout

In pursuit of a non-jiggly midsection, I have spent an inordinate amount of time on workouts that target the core, or trunk, muscles -- particularly my slacker abdominals, which would rather not tighten, twist or lengthen.

Cursed with a short attention span, my abs and I can endure only so many stomach crunches and elbow-to-opposite-knee sit-ups before getting bored. Recently, I tried a new kind of core class that was challenging enough to keep my mind from wandering -- Pilates atop a device that looked like a stability ball sliced in half.

The fitness tool, called the BOSU Balance Trainer, is turning up in gyms across the country and is used by the U.S. Ski Team, the Dallas Cowboys and New York Knicks, among others. In California, BOSU classes are offered at such gyms as Crunch, Equinox and Bally Total Fitness; recently, BOSUs have been picked up by smaller facilities such as the Core Conditioning studio in Westminster, where personal trainers use the BOSU in workouts with clients.

The pairing of BOSU (which stands for “Both Sides Up” and is pronounced bo-sue) and Pilates is a recent phenomenon, said Dustin Schnabel, a project manager for Fitness Quest Inc., an Ohio-based company that distributes the BOSU. He did not know how many gyms currently offer such classes. The combination seems natural, he said: “It’s a no-brainer. Just the whole Pilates foundation of movement is synonymous with what we’re saying the BOSU is used for -- balance is the foundation of all movement.”

BOSU-Pilates classes are part of a larger trend of fitness fusion, in which gyms are trying to hit on the right combination of popular offerings. Find the right blend, such as Jazzercise, and a new craze is born. Lately, ballet spin-off classes have been taking off, along with combination yoga and Pilates classes, which, at one Chicago studio, has been dubbed “Piloga.”

Pilates is the country’s fastest-growing fitness activity, with 4.7 million participants in 2002, according to a study by American Sports Data. I take an occasional Pilates course but never thought of trying the moves on a balance trainer until, searching online for BOSU classes, I came across one at the John Garey Pilates Studio in Long Beach.

Garey is a certified instructor for an updated form of Pilates known as the Stott Method, which designs exercises that emphasize the natural curves of the spine and muscles around the joints. He learned BOSU-Pilates from Stott Pilates founder Lindsay G. Merrithew and began offering the class at his studio nine months ago, intrigued by the way that the balance trainer forces people to work harder. Individual classes at Garey’s studio cost $25, or 10 classes for $200 (for more information, go to www.johngareypilates.com, or call [877] 774-5283.)

In a Pilates class, on a mat, participants don’t always feel their abdominal muscles working, Garey said. But on the BOSU, “you can always feel it where I’m asking you to feel it. You can’t do this without working your abs. There’s just no way.”

Even basic crunches are hard for beginners on the BOSU. You have to mold your back to the half-moon shape, and on the wobbly surface, you have two choices: Tighten your stomach muscles as if they were being pulled taut by marionette strings or fall off the dome when you try to raise your torso.

Garey’s small studio is painted in shades of aquamarine and has no mirrors. The BOSUs are placed on top of padded benches that are used in other Pilates sessions. On a recent night, only three other students showed up for the Wednesday class. Garey tries to limit classes to a maximum of six, so he can work with each student individually.

One of the first moves called for us to sink into the BOSU, lower backs against the dome, hands behind the head, feet planted and stomachs clenched to keep our bodies in a slanted position. “Immediately when you get into this position,” Garey said, “you’re going to feel like you’re working harder than you’ve ever worked before.”

From there, with my upper body still, I tried to follow his instructions to tilt my pelvis up and down, while, theoretically, drawing in my belly button. I managed little lifts, but, even for an experienced BOSU user like me, it was tough.

With my mid-section starting to strain, I began to use my feet for momentum but got busted. “It should all be abs,” Garey said. I was relieved that he didn’t include some of the harder Pilates moves in the class, such as the one in which, sitting on a mat, clutching your knees, you roll backward in a semicircle and then forward while keeping your feet from touching down. He modified other moves for the BOSU, such as the “100s,” which are usually done lying on your back, upper torso lifted, then both legs lifted at a 45-degree angle if possible.

We did the 100s on our knees, hip-width apart. On the BOSU we leaned back, at about a 45-degree angle, while inhaling, then pulled up on the exhale. We repeated the move for a total of 100 counts, long enough to make my upper thighs start shaking.

Garey ended the class by having everyone move to the floor for jumping squats and other cardio moves on the BOSU. Each of us, including Garey, fell off at some point, laughing.

The class would be a bear for beginners in Pilates or BOSU, and would leave most novices sore and sweaty. For people like me, who regularly train on the BOSU, it was fun to try new moves, even ones that didn’t send my heart racing. The class flew by, and afterward, as Garey had warned, I felt my stomach muscles, every contour of them. I’ll keep working on the moves at my own gym, where BOSUs are available in the stretching area.

After class, Eileen Gallagher, 48, a regular, said the BOSU had added a new twist to her usual Pilates workout. “You don’t get bored. I think it’s the most effective 50-minute workout for your abs, and particularly the obliques [on the side of the midsection], that you can do.”

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Times staff writer Renee Tawa can be reached by e-mail at renee.tawa@latimes.com.