Long used by Soviet athletes, kettlebells are catching on in gyms across the United States. They look like cannonballs with handles, and trainers say they melt fat and build muscle definition faster than traditional free weights. "More and more people are looking at this as really good functional training," says Terry Malone, director of physical therapy at the University of Kentucky. Kettlebell users work out by swinging the weights, which range from nine to 88 pounds each, with one or both hands while performing squats and other dynamic movements. "It trains the body as one unit, rather than isolating body parts," says Sarah Lurie, founder of Iron Core ( ironcorelajolla.com ), a California gym devoted to kettlebell training. Look for classes at Equinox gyms ( equinoxfitness.com ) or buy weights and workout videos on amazon.com .