Easy conversation and banter filled the air as a dozen boot campers finished jogging a 5:30 a.m. warm-up lap around Himmel Park.

"Today's going to be a hill day," said Paul Rose, the easygoing instructor who owns Urban Athletics Boot Camp.

Some groaned good-naturedly before running up and down a modest hill on grass still damp from an early-morning watering.

At the bottom, participants selected weighted burlap sacks to do timed keg tosses.

"This is the only alcohol-related movement we do," joked Rose, who says he picked up that movement from watching "The World's Strongest Man" competition.

Urban Athletics is one of more than a dozen boot camps in town that attract determined Tucsonans in the wee hours of most mornings.

These people haven't enlisted in the military. They actually pay for this.

Boot camps started appearing in Tucson parks and gyms in the early '90s, and their popularity continues to increase. The camps in Tucson meet mostly in parks at sunrise or in the evenings. Some meet at health clubs indoors.

All provide cardiovascular benefits and work every muscle group through high- and low-intensity exercises such as push-ups, squats and lunges.

Most boot camps go in four-week cycles, although many participants continue year-round.

Ron Holland, who owns SWAT Fitness and is a former Air Force SWAT commander, just may be the godfather of Tucson boot camps.

Holland, 62, started teaching boot camps on the northwest side in 1990. He now runs three SWAT locations, which offer small-group and personal-training classes, in addition to boot camps.

Boot camps remain one of the most popular forms of group fitness, according to the San Diego-based American Council on Exercise, a nonprofit organization that promotes active lifestyles and certifies personal trainers. ACE has about 40,000 certified trainers worldwide.

Boot camp programs are easy to put together and take little equipment, and participants can see big results, said Pete McCall, an exercise physiologist and ACE-certified spokesman.

"I think sometimes you get more results and better adherence (with boot camps)," McCall said about the supervised approach and camaraderie instilled in a typical boot camp. "They kind of hold you accountable. You think, 'If they're going to be there at 6 a.m. and be miserable, then I should probably be there.' "

McCall said participants can burn up to 10 calories per minute, along with benefiting from a higher-than-average calorie burn for two or three hours after the workout.

Boot camps are great for anybody who needs extra motivation.

"It provides structure; it provides guidance," McCall said. "It's also for people who get bored in gyms. One of the biggest complaints I hear is they don't like traditional health-club equipment and classes. But they don't have time to do competitive sports as an adult."

Tom Tronsdal joined the Raena Fitness camp about eight months ago. He gets up before sunrise and makes his way to La Madera Park three times a week.

"Going is now the easiest part," said Tronsdal, a 40-year-old partner in Canyon Fence Co. "If I don't go, I'm really bummed. I really don't like it when I miss it."

He said it's understandable to be intimidated at first by boot camps, but they're really no different from any other new activity.

"Whatever you do, there's always somebody better than you," Tronsdal pointed out.

The 40-year-old started running when he was 33 and has completed nine marathons. He turned to boot camp because he wanted to improve his running times.

"I was running races, and I wasn't getting any faster from just doing the same thing over and over again," he said. "I ran a marathon when I first started working with Raena, and I did OK. "In about six months, I ran the (Boston Marathon). I noticed a 22-minute improvement."

Tronsdal is used to being one of the few men in his sessions.

And that's too bad, said Raena Isaacson of Raena Fitness.

"I think guys get stuck with the philosophy that they can't get a good workout in boot camp, or they might be intimidated," she said. "Every time I get a guy, he stays. Once they try it, they get it."

Laurie Jackson, a personal trainer with the Tucson Racquet and Fitness Club, hopes to get a "whole slew" of people at her upcoming boot camp.

The 37-year-old group-fitness instructor plans to offer a boot camp at 5 a.m. three times a week toward the end of summer.

Participants won't have to be a member of the club to join.

"It's a relatively inexpensive way and a time-saving way to change your body and have a lot of fun doing it," Jackson said.

Of course, boot camp isn't for everyone.

McCall, of the American Council on Exercise, said people should have a basic level of fitness before they attempt boot camp.

Someone who hasn't worked out in 10 years, for example, shouldn't jump right in, he said. "You're going to have severe consequences."

FINDING THE RIGHT BOOT CAMP

Ron Holland of SWAT Fitness said he has noticed a lot of changes in boot camps since he started one in Tucson 20 years ago.

"A lot of boot camps have been watered down, and there's a boot camp on every corner now," he said. "Some of them are professionals - some are not."

Here are a few tips on how you can decide if you've found a boot camp that's right for you.

• Decide whether you want your boot camp to be indoors or outdoors. Dirt, bugs and bad weather can deter some.

• You should do most of the talking during your first conversation with a potential trainer. The trainer should ask you about your goals, limitations and expectations.

• Take advantage of the free trial that many camps offer to see whether you like it.

• Certifications are fine, but they're only a small part of what makes a trainer.

• Notice how the trainer establishes rapport with the clients. Does he pay attention to everyone, or does he single people out?

• "Does he look like a trainer?" Holland asked. "A lot of trainers don't practice what they preach."

To yell or not to yell?

When military recruits enter boot camps, they often endure weeks of relentless screaming, yelling and belittling.

And some high-profile trainers, such as Jillian Michaels from TV's "The Biggest Loser," are renowned for their tough-talking, hard-core approach.

Local boot-camp instructors say their camps are different.

"We don't scream at people," said Angie Rios of Precision Personal Training.

"The only reason (Michaels) is doing it is because it's on TV. I think it's a way to get people to watch."

Tom Tronsdal, who works out with Raena Isaacson of Raena Fitness, thinks yelling is counterproductive.

"Raena pushes, but she doesn't yell," he said. "She realizes people have already made the most difficult decision by showing up. Most people are trying to improve themselves - why would you want to be yelled at?"

Pete McCall of the American Council on Exercise said that certain TV shows exaggerate boot camps' tough approach.

"Personal trainers should not be demeaning or physically reckless," he said.

He also said he's not surprised that the TV shows' participants lose weight quickly, noting that participants in shows such as "The Biggest Loser" have it easier than, say, the typical working mom.

"You can take anybody out of their daily life and get results," McCall said.

SOME TUCSON-AREA BOOT CAMPS

If you're interested, call or sign up online in advance.

Bodyzen Boot Camps Fitness and Training

• Where: Jesse Owens Park.

• When: 6-6:45 a.m. Mondays, Tuesdays, Thursdays and Fridays; 5-5:45 p.m. and 6-6:45 p.m. Mondays-Fridays.

• Cost: $100 three times a week for four weeks; $150 five times a week for four weeks.

• More info: www.bodyzenbootcamps.net; 808-9827.

Boot Camps In Tucson by Precision Personal Training

• Where: Himmel and Udall parks.

• When: 5:30-6:30 a.m. and 6-7 p.m. Mondays-Fridays at Himmel; 5:30-6:30 a.m. and 6-7 p.m. Mondays-Fridays at Udall.

• Cost: $150 three days a week for four weeks; $200 five days a week for four weeks. The first Monday of each new session every four weeks is free.

• More info: 323-3488; www.bootcampsintucson.com

Brown's Boot Camp

• Where: Reid Park, Mountain View High School, Wildlife Ridge Park in Rancho Vistoso, CDO Riverfront Park and Westward Look Resort.

• When: Mornings and evenings Mondays-Saturdays. Go online for details.

• Cost: Variety of packages that break down to $12.45 an hour.

• More info: brownsbootcamp.com; 339-8878.

Cooper Boot Camp

• Where: Himmel Park.

• When: 5:30-6:30 a.m. Mondays, Wednesdays, Fridays. Other sessions at other parks will begin in the fall.

• Cost: $80 a month for unlimited sessions.

• More info: cooperbootcamp.com; 400-7474.

Old Pueblo Gymnastics Academy Adult Boot Camp

• Where: 7670 E. Wrightstown Road.

• When: 5:30-6:30 a.m. Tuesdays, Thursdays and Fridays (the next class begins Aug. 3).

• Cost: $31 a year to become a member, then it's $90 a month.

• More info: oldpueblogymnastics.com; 628-4355.

Performance Fitness

• Where: 2951 N. Swan Road.

• When: 6-7 a.m. Mondays, Wednesdays and Fridays; 6-7 p.m. and 7-8 p.m. Mondays and Wednesdays; and 9-10 a.m. Saturdays.

• Cost: Ranges from $35 for club members for four Saturday sessions to $125 for non-members for 12 sessions.

• More info: www.performancefitnesstucson.com; 325-5455.

Raena Fitness Boot Camps and Running

• Where: La Madera Park.

• When: 5:30-6:30 a.m. Mondays, Wednesdays and Fridays. 5:30-6:30 p.m. Tuesdays and Thursdays will resume in the fall.

• Cost: Prices vary from $10 for one class to $84 for three days a week for four weeks.

• More info: www.RaenaFitness.com; 349-4716.

SWAT Fitness

• Where: 3820 S. Palo Verde Road; 6127 N. La Cholla Blvd.; 7000 E. Tanque Verde Road.

• When: 5:30-6:30 a.m. Mondays-Fridays east and northwest sides; 5 a.m., 9 a.m. and 6 p.m. (indoors) south side.

• Cost: $199 a month, or $150 if you sign up for a year. First-time campers must take a two-hour, $149 one-on-one introductory session to learn how to use kettlebells and other skills. It also includes a body assessment, nutrition consultation and goal setting.

• More info: www.swatfitness.com; 579-6791.

Urban Athletics Boot Camp

• Where: Himmel Park and CDO Riverfront Park in Oro Valley.

• When: 5:30-6:30 a.m. Mondays, Wednesdays and Fridays at Himmel; 6-7 a.m. Mondays, Wednesdays, Fridays at Riverfront.

• Cost: $149 for monthly Peak Performance package.

• More info: www.urbanathleticsbootcamp.com; 445-8000.