Do you want the strength of undefeated boxer Laila Ali or the body of heavyweight champion Lennox Lewis? You don't have to step into the ring to get a great workout. Boxing classes are becoming the norm in many health clubs and fitness centers across the country. Participants are learning what boxing enthusiasts have known for years--that boxers are some of the most highly conditioned athletes competing in sports today, and that if you follow some simple procedures, you can build stamina, tone your muscles and burn calories. "Boxing is one of the best exercises. You work all of the muscles in the body," says Terrence Blackmoore, a trainer at Gleason's Gym in Brooklyn. "More people are becoming interested in the sport as exercise. Women are crazy for boxing right now ... It's a whole-body workout." For the most part, women are behind the increased interest in the sport, experts say. As more women get their hands and wrists wrapped and lace up the gloves in amateur and professional boxing, health-conscious women are beginning to use boxing for fitness. "I always wanted to learn kickboxing for fitness," says Mea Robinson-Davis, who takes a class at Chicago's New City YMCA. "It's an excellent cardiovascular workout, and you learn a skill." There is a difference between boxing professionally and working out alongside your fellow classmates in the safety of a health club. Although professionals are at greater risk for head and neck injuries, most health and fitness experts urge newcomers to confine their fisticuffs to the gyms, where boxing classes will help to improve your cardiovascular fitness, flexibility and coordination. "I think anybody who tries it knows that it takes a lot more work than anything else," says Terry Southerland, a trainer and boxer who teaches boxing classes at Crunch Fitness in New York. "Nothing takes more energy."