NEW YORK (Reuters Life!) - Call them Swiss balls, Pilates balls, physio balls, exercise balls, balance balls, yoga balls or body balls.
Stability balls by any other name would still be the same hardworking multi-taskers of the fitness world.
"They can be used for balance training, for core training, with or without weights and for resistance training," Dr. Christina A. Geithner, of the American College of Sports Medicine, said of those big, colorful spheres that brighten the corners of workout rooms everywhere.
"They are fun, versatile, inexpensive and relatively easy to use," she said. "And they come in different sizes for different sized individuals and for different uses."
When the balls first bounced into gyms, they were dismissed by many professionals as a fad. But their seemingly limitless adaptability, reflected in their many monikers, has solidified their status as the multipurpose work horses of exercise.
"You can use them in yoga and Pilates, in cardio and strength training," said Stephanie Vitorino, group fitness manager at Equinox, a national chain of luxury gyms.
"The stability ball works for the senior doing low-impact cardio, the pregnant woman strengthening her core, and the pro-athlete working on peak performance," she said in an interview from Woodland Hills, California.
The stability ball was rolled out in the early 1960s as a toy manufactured by Italian Aquilino Cosani and sold mainly in Europe as the Gymnastik.
It morphed into a rehabilitative tool in the hands of Dr. Susanne Klein-Vogelbach, who ran a physical therapy school in Switzerland.
The fitness industry discovered its possibilities in the 1980's, and the balls were introduced in the United States in 1989.
For Vitorino, who teaches cardio and strength conditioning classes, the ball serves as a nifty equalizer.
"Anyone in the class, beginner or top-level, can use the ball because any movement can be progressed," she explained.
"In pushups, for example, the beginner can place the ball closer to the midline, while the more fit people can place it down by their shins where it's more difficult," she said.
"So the same exercise can be done by the beginner and the person who's really strong."
Vitorino says she loves incorporating the stability ball because she knows that everyone will walk away from the workout feeling that they've worked to their ability.
Stability balls vary in diameter from 55 to 85 cm (22 to 34 inches). Vitorino says it's safest to choose the size that allows you to sit on it in an erect posture with your hips and knees at 90 degrees.
But even here there's room for play.
"To stretch, a smaller ball will get you more range of motion. For more stability you'd probably want a larger ball," she said.
"Stability ball is a funny name because the balls are unstable. But they create stability. It's kind of a contradiction. It's an unstable surface so the stability comes from you," Vitorino explained.
"You have to activate your core; you have to engage many muscle groups to stabilize your body in various movements," she continued.
"Everything comes from the center," she said. "As the world is going around, you are stable in the center of it."