But calisthenics only work if you discipline yourself to do them regularly, which is one reason for the popularity of the "drop and give me 20" motivation offered by the new boot camps.

"We hold your hand and kick your butt at the same time," says Patrick "Sarge" Avon, owner of The Sergeant's Program, which runs 6 a.m. and 7 a.m. workouts at 25 sites--mostly parks and playgrounds--around the Washington, D.C. area. "It's like personal training for a group, where we push you harder than you'd push yourself."

About 500 people--evenly divided between men and women, ranging in age from about 25 to 50-- work out with the Sergeant's Program. Exercisers must first enlist in a three-week Boot Camp that meets five mornings a week for 45-minutes per session and costs $345. At the end of "camp," students take a military-style fitness test, which about 65 percent pass. Graduates can join the Sergeant's Maintenance Program, a five-morning a week, hour-long workout, for $80 to $95 per month. Those who fail can re-up for Boot Camp, but at the lower fee of the Maintenance Program.

"Lots of people don't want to go to gyms," says Avon, who offers boot camp and other fitness programs to corporations. Basic training offers an appealing, fresh-air alternative to the noise, mirrors, intimidating equipment and hard-body clientele at many gyms, he says.

In addition to shaping up the body, military-style workouts also pay off in mental fitness, says former SEAL Smith, who leads classes for the Sergeant's Program near his home in Annapolis. "The unbelievable amount of confidence you will gain in your abilities will change your life," he writes in his just-released "Complete Guide to Navy SEAL Fitness" Five Star Publishing, 1998). "Your boss, friends and co-workers will see a lean, fit, self-assured person who has the attitude that anything can be accomplished."