When Dawn Ruppert shouts, "Friends don't bring friends to this class!" at the opening of her Balanced Body Conditioning exercise class, even seasoned athletes among the newcomers are inclined to sneer, "Sure, whatever." But when the workout ends 75 minutes later (sometimes more, if Ruppert's in the mood), the snickerers are too pooped to smart-mouth. A fitness fanatic, Ruppert has taught exercise classes at different St. Louis venues for two decades. For the past two years, she's laid down her fitness gauntlet at the Pilates & Yoga Center of St. Louis. Her twice-weekly "conditioning" class, which Ruppert designed herself, defies a catchy description and is best summed up as a hybrid of yoga, aerobics, Pilates and weight training. (Who knew a person could lift weights while standing in Eka Pada asana?) Women of all ages sweat gallons to the tunes of Prince and Taylor Dayne, then pop Advil for two days following. Men, on the other hand, have a sketchy track record with Ruppert. "We'll get one occasionally -- we even had a triathlete -- and he'll never come back!" says she.