Should you step away from that Swiss ball? Unstable surface training can build balance and stability -- but squatting, lunging, and curling on wobble boards and BOSUs actually may be doing the rest of your workout a disservice, according to new research in the Journal of Strength and Conditioning Research.

The study found that performing half of the exercises in a training program on a BOSU ball not only didn't offer a group of Division II soccer players any fitness advantage in terms of speed or agility, it actually decreased their jumping ability. (If you've been sidelined by aches and pains, pick up The Athlete’s Book of Home Remedies for 1,001 doctor-approved fixes for every sports ailment.)

The new findings back up research first done by Eric Cressey, president of Cressey Performance in Hudson, Massachusetts, and the author of The Truth About Unstable Surface Training. In his study published in the Journal of Strength and Conditioning Research in 2007, Cressey found that adding unstable surface training -- even when it took up just 2 percent of a strength and conditioning program -- curbed overall speed and agility gains. On a 40-yard sprint, for example, the regular training group improved their times by 3.9 percent, while the unstable group improved by only 1.8 percent.

But you don't need to deflate your Swiss ball -- just understand how to use it. (For a quick workout that will target every area of your core, check out The Best Abs Workout You’ve Never Done.)

Balance vs. Stability
"Balance" and "stability" are often used interchangeably, but they're actually different things. Stability -- as defined by exercise scientists -- is your body's current state of resistance to acceleration against you. That constantly changes based on your body mass, relationship to the ground, and the forces around you. Think of a professional sumo wrestler’s heavy-set body and low, wide stance -- and now imagine trying to knock him over. That’s a stable athlete.

Balance, however, is a skill that can be practiced and improved. It's the ability to maintain equilibrium, particularly in less-stable states. Standing on one foot, for example, challenges your balance. You're also less stable in this position, since someone could easily topple you over.

Unstable Devices and Balance
Unfortunately, Cressey says, unstable surface training only improves your balance on unstable surfaces. “Balance is incredibly skill-specific,” he explains. “So a football player who can change directions on a dime isn’t necessarily going to have great balance throwing a baseball or riding a surfboard. The number one thing you can do to improve balance is to participate in activities you want to get good at.” (Click here for new research that can help you Be The Star Of Your Sports Team.)

If you're looking to improve your balance in everyday life -- standing on your toes to grab an item on a high shelf, opening a door when your hands are full -- something as simple as standing on one foot while you brush your teeth can help, Cressey says.

How Unstable Devices Can Hurt Performance
The problem with training on unstable devices -- and the reason they hinder strength improvements -- is that standing on unstable devices teaches your body to compensate in undesirable ways.

For one, unstable surface training tends to recruit the wrong muscles, Cressey says. The muscles you’re trying to train -- called agonists -- end up firing less. Those on the opposite side of the joint -- the antagonists -- fire more in an effort to stabilize the joint in an unstable position.

That's a problem if your goal is strength. "There's two different ways we can get strong,” Cressey says. It happens either by firing the agonists or by shutting off the antagonists, which act as a kind of braking force. If the antagonists are activated, the agonists won’t get as strong. (Speaking of becoming stronger, read our 20 Best Training Guides.)

In short, your body’s braking action in an effort to achieve balance gets in the way of strength improvements.

The problem is similar when it comes to power. Unstable surfaces tend to cause feet to excessively pronate (roll inward), flattening the arch of the foot, in an effort to stabilize the body. That position puts lower-body muscles at a mechanical disadvantage, as they need the arch of the foot to be in a good position to propel the body. Otherwise, you’re stuck in deceleration mode.

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Where the Balls and Boards Are Useful
Unstable devices can be effective at training joint stability, which has some notable applications. Research shows stability devices are effective for rehabbing ankle sprains, for example.

And Cressey touts them for training upper-body stability. The difference is that the shoulder is inherently a less-stable joint than the hip, because of its relationship to the ground. "If a joint isn't stable, our brain knows to shut down our strength so that we don't risk injury," Cressey says. "So joint stability allows us to train pain-free, building strength as we go."

Shoulder stability is also helpful in everyday life. "Think about carrying a bag of groceries in one arm," he says. "You're unstable, but it's a lot different than walking on an unstable surface." The bag of groceries destabilizes your shoulder joint while the ground stabilizes your hip joint. So in this case, some additional stability in the shoulder joint would be helpful.

To train shoulder stability, Cressey suggests Hips-High Hand Switches. Watch David Jack, director of TeamWorks Fitness in Acton, Massachusetts, show you how to perform the move in the video below.

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Humans typically do their thing on solid ground, Cressey says. So lower-body training on unstable surfaces may simply be irrelevant to everyday life as well as athletics.

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