Harry Mataras, a 37-year old New Yorker, doesn’t go in much for gyms but has been a lifelong fan of boxing. “You see fighters with incredible physiques, with no weight training involved,” he says. As with many men, for Mataras, aerobics was out: " the time I’d get the step, the class was on to the next one."

Until recently, the phrase “women and boxing” evoked activities best confined to sleazy joints in Times Square. Most men picked up the sport only if they were aiming for the Golden Gloves. But now, a handful of forward-thinking fighters and trainers have wedded aerobics and boxing to create a gym-friendly new breed of classes that attract at least as many men as women. At Bodies in Motion, an L.A. gym, Cramer and her classmates don lightweight gloves and jab, slide and crunch their abs in an Executive Boxing class. At New York’s Equinox gym, Mataras happily sweats up a storm in Aerobox classes, created and taught by Michael Olajide, 28, a graceful ex-middleweight contender.

Olajide, whose long hair and soothing voice clash with the Central Casting image of a tough-talking retired bruiser, calls his class “aerobics gone hard core. It’s back to basics.” Taught in an airy, mirrored room, Aerobox is an hour of astonishingly fast punching exercises and rope jumping that leaves the muscular batch of students (60 percent are men) red as beets after a few minutes. Aerobics boxers seem especially pleased by the cross-gender appeal of the classes. “Men don’t really have an aerobic sport besides running, and they don’t watch Jane Fonda videos,” says Olajide. “Boxing is mentally challenging, and it offers the aggressive end of things.” Manly, yes, but women like it, too: " They really get into it; they really go for the kill," says Klaus Price, a trainer who cocreated Executive Boxing. For a better left hook, advises a woman at Bodies in Motion, think of your punching bag as an ex-boyfriend.

Like any aerobics class worth its sweat, Aerobox and Executive Boxing will soon be out on video, enabling home exercisers across America to spar with their hanging plants. Olajide hopes Aerobox will cross back into the ring, too: boxers can benefit from the aerobic workout, and instruction offers them an alternative career when their pro fighting days end. The ex-fighter even sees Aerobox serving the champs of the future. When boxing grew in popularity a few years back, Yuppies surged into neighborhood gyms. Now, he hopes, aerobic boxing will lure them back into upscale gyms and free up trainers to create tomorrow’s contenders.