Balance is everything, says [Hunter Joslin]. "Across all of fitness, no matter what sport, balance is about those small stabilizer muscles in the core, and they're the least exercised muscles in the body." One of Joslin's favorite moves for core stability is to throw the medicine ball while standing on the Indo board. Lifting small hand weights while balancing is another.

The Vew-Do Board ($89.95, www.vew-do.com) started out as a piece of training equipment for snowboarders more than 10 years ago, but has grown into its own sport: balance boarding. Vew-Do boards have heavy skate and snowboarder appeal, but there is a whole line, the Contact Series, designed for the beginning balance trainer. The Balance 101 board provides the basic fore and aft movement on a shorter board, offering greater control of movement. Primarily used to introduce people to board training or for rehabilitating injured athletes, the Balance 101's increased control allows for a less- wobbly workout. "Knowing you can stay up is half the battle," says Vermonter Brew Moscarello, the board's inventor. "Balance training betters your reaction time -- even if you only do it a few minutes a day. It improves your muscle firing and raises your overall body awareness, which is necessary for any sport."

The big board on the block these days, however, is the Reebok Core Board ($189, www.reebok.com, click on "store" and do a search for core board). It sits five inches off the ground and is about two feet wide. The one-piece unit is not light; tipping the scales at about 28 pounds, it requires upper body strength just to lift it. Initially developed by Reebok as a physical therapy tool to help rehabilitate professional and Olympic athletes, its popularity among trainers has made it a staple in core workout classes.