CHICAGO - What if you could burn fat while shaking a martini? Actually, it's your body that shakes like a martini on a new type of fitness machine that's generating lots of buzz and celebrity use. Even NASA has tested the concept.

Trainer Michela Rossi watches Amy Allen as she exercises on a Power Plate fitness machine Wednesday, May 23, 2007, at the Power Plate Institute in Chicago. [AP]

These machines use vibrations to tone muscle and claim to do it faster. Aggressive promoters also say the equipment improves flexibility and strength, reduces pain and stress, builds muscle and reverses osteoporosis.

However, researchers warn of possible injuries ranging from back pain to cartilage damage. One even warns that the high-powered jiggling might harm the brain. They say the science is thin and too little is known about the long-term effects of such powerful vibrations.

Still, NASA is studying vibration as a possible tool for reducing muscle atrophy and bone loss during astronauts' long, weightless trips in space.

And users of the equipment love the sensation and the quick workout. Workout times are reduced by two-thirds, advocates say, a claim that appeals to busy professionals, mothers of young children and just about anyone who shuns exercise.

"I feel kind of tingly and a little like I got off a ship, kind of shaky but in a good way," said Amy Allen, a 40-year-old working mom in Chicago, after a 25-minute workout on the Power Plate, one of the higher-end brands. "I'm hoping this is the solution to help me get that extra weight off."

The Power Plate vibrates 20 to 50 times a second in three directions, increasing g-forces on the body, and according to the Northbrook, Ill.-based company of the same name. The company says that raises the effectiveness of lunges, squats and other exercises done while standing on it.

The workout is not aerobic; it's more like weightlifting without weights.

"You don't really feel like you're working that hard, but then you get that sweat going and once the vibration stops, you can really feel it in your legs or upper body," said Michaela Zakheim, 45, who uses the machine at a fitness center in her Lincoln Park neighborhood.

Power Plate sells models for home and gym at prices ranging from $3,000 to $10,500. Motors in the base make a low humming noise. Controls adjust the duration and intensity. The machines weigh 264 to 500 pounds and have handles to hang onto.

Fitness trainers love them, but some users don't like the fact they can't read or watch TV while working out on them, said Craig Bradley, general manager of Holmes Place, an upscale Chicago health club that has four Power Plates. Doubts also stem from memories of the belt vibrators popular 50 years ago.

Others have been won over though.

"I think the machines are as good as the imagination of the person using them," Bradley said.

Dozens of companies have entered the market, including Soloflex which has sold more than 30,000 of its $295 vibrating, skateboard-like, handle-free platforms in less than three years, said Jerry Wilson, the Hillsboro, Ore.-based company's CEO and founder.

"We get reports back that it helps people with incontinence," Wilson said. "Their aches and pains have gone away. They're stronger. They sleep better. It has basically the same effects as if they'd started an exercise program."

A study at NASA's Johnson Space Center showed that the use of a vibration platform during exercise squats made muscles work more, but it didn't look at whether vibration makes athletes run faster or jump higher.

1

2