NEW YORK - Zeus the pit bull helps his owner slog through interval training and military crawls, Goldie and her master enjoy Tai Chi together and Izzie the three-legged shih tzu can't hike up the mountain but she acts as a hand weight for her owner's bicep curl.
Experts say a dog may be man's best fitness friend, and dog-and-master workouts don't have to be limited to a run on the beach or a Frisbee toss.
"Unlike humans, their motivation never peters out. Dogs don't drop off one by one, like other fitness buddies," said Dr. Marty Becker, an Idaho-based veterinarian and author of "Fitness Unleashed: A Dog and Owner's Guide to Losing Weight and Gaining Health Together."
Becker cited statistics he said show that 56 per cent of dogs and cats and 66 per cent of people are overweight in America.
Bow Wow Bootcamp, Tai Chi Wa Wa and Pupilates, are a few of the group fitness class offered to humans and their dogs at K9 Fit Club, which has locations in Illinois, Tennessee, Pennsylvania and Florida.
Founder Tricia Montgomery was working for the Chicago Veterinary Medical Association when the idea of a gym for people and pets occurred to her.
Behind the cute names is a serious purpose.
"We are not just a bunch of people getting together with our dogs," said Montgomery. "Our programs are designed by certified trainers and psychologists."
Fitness professionals and animal trainers lead the 55-minute classes, she said, which are limited to eight to 10 people and their pets.
"Every one of the classes we do follows a complete (client) assessment that includes a behaviour assessment for the companion animal," Montgomery explained.
For people without a dog, the gym will work with a shelter to provide one, she said.
"Some people I deal with are morbidly obese. They're intimidated by gyms," she said. "The dog's not going to judge you. And they'll never cancel on you."
San Diego, California-based fitness trainer Tamilee Webb incorporates her three-legged shi tzu Izzie in much of her daily regime.
"If I go for walk or hike, she's in a doggy backpack to add a little extra weight," said Webb. "I'll do squats, lunges and pushes and she'll still be on my back."
Webb is the creator of the "Buns of Steel" and "Abs of Steel" DVD series. She has also taught a pooch boot camp.
"I would take a group of six to 10 mostly women and their dogs, big or small, on a walk," she said. "Then we'd stop and do exercises, sometimes with rubber tubing, sometimes with the small dogs as resistance."
At least 39 per cent of American households include at least one dog, according to the Humane Society. A 2011 study from Michigan State University found that people who owned and walked their dogs were 34 per cent more likely to meet the federal benchmarks on physical activity.
"I think a pet gets you out to be active," said Webb. "Working dogs need at least 30 minutes of exercise and two hours of activity," she said. "Little dogs don't need that much."
Webb has taken bigger breeds and their owners up and down stairs, on runs, and in pools.
"In San Diego, you can take a dog surfing," she said. "And there's Doga (yoga for dogs)."
Becker, who has four dogs, as well as some cats and horses, favors a back-to-basics approach to human-dog fitness.
"The great thing about exercising with a pet is that you don't need a gym and you don't need expensive equipment," he said. "All you need is a good pair of shoes and a walking leash and you're out the door."
For dogs, it's all about the cardio, he explained.
"There are no bikini seasons for dogs, no trying to get into last season's Levis," he said. "And dogs do their own stretches."