Even if you could teach an old dog new tricks, Sugar wouldn't be able to learn. The 12-year-old beagle mix used to love running around owner Todd Morrison's backyard in West Virginia. But now, when the once-lean Sugar lies on her back with all four paws in the air, she struggles to roll back onto her feet.

Sugar is not the only dog that cannot roll over. As the number of obese Americans rises, so does the number of their obese canine companions. With about 25 percent to 40 percent of American dogs overweight and owners too busy to attend to the activity needs of their pets, doggy fitness camps have popped up around the nation to tone up man's best friend.

With a strict diet and streamlined exercise program, these dog spas and exercise camps try to get dogs and their owners into the groove of healthy eating and regular exercise.

Morrison said Sugar's girth increased as she aged and ate too many snacks offered by loved ones like Morrison's grandmother, who lives next door. Morrison said that he was concerned about his dog's weight, but that it was difficult to resist throwing his best friend a snack or two during the day.

"She's just kind of a fat thing that sits in the corner, but we still love her," Morrison said. Though he has considered trotting Sugar off to one of several new doggy fitness camps, Morrison said he felt uncomfortable watching her struggle athletically.

Dr. Munir Kureshi, a veterinarian in Cupertino, Calif., estimated that 80 percent of his canine patients were overweight or obese. Those conditions can cause severe joint problems, like arthritis.

Most dogs gain weight after being spayed or neutered. But by the time a dog reaches age 6, the equivalent of age 40 in humans, the owners need to deal with any weight issues, veterinarians and animal experts say. Kureshi said the dogs' habits mirror those of their owners, and the owners can be in denial about their pets' weight issues.

Ilene Robbins began her doggy day-care service, Camp Ilene, in the early 1990s. The rise of obesity in dogs has increased her business and caused her to change some of her exercise techniques. With overweight or obese dogs, she is cautious about overexertion and exercises that can damage a dog's joints.

Robbins said owners can be reluctant to acknowledge their dogs' problems. After noticing one client's dog was a bit chunky, she said, the woman claimed her dog was "just a big girl" with "a lot of hair."

"Oh my God, your dog is overweight," Robbins recalled thinking. "It's not the hair."

Winnie Wong, a Web designer from Pleasanton, Calif., said she had grown concerned about her 2-year-old pug, Shelby, when three separate strangers approached her and remarked about what a "cute and fat dog" she had.

"I'm not fat, but my first reaction was, 'How did I not see this?' " Wong said. "It was like if someone told me my kid was fat. It was like, 'Hey, how dare you?' It took a few times before we came full circle from denial to anger."

With a special diet and stricter exercise regime — much like Shelby would receive at a doggy fitness camp — the pug shed the three extra pounds and became much more spunky, Wong said.

Ami Moore, founder of Chicago's Doggy Do Right 911, said she started a dog spa because "dogs mirror obesity in people." Moore added that if an owner eats junk food, the dog probably does, too.

Moore, who eats only raw meat and dairy products herself, said her 31-day program to help dogs shed extra pounds includes three walks a day on a treadmill and a special diet — the recipe is a company secret. All dogs must have a note from a veterinarian certifying the dog as overweight or obese. While Moore claims her dog clients lose all the weight they need to in a month, she said it was up to the owners to maintain the dog's lifestyle.

Sue Bartlett and her husband, who raise hunting and show beagles at their home in Erie, Pa., lost a beagle named Molly five years ago, in part because of her weight problem. The 45-pound beagle — an average beagle weighs 16 to 21 pounds — was often confused for the droopier and heavier-set Bassett hound. When Bartlett tried weaning Molly off her favorite snack, bologna, she noshed on rat poison instead.

Low-carb and low-calorie food abounds in pet stores, but Robbins said it is particularly important for dog owners to be careful at snack time.

"In America, people see food as a physical manifestation of love, and instead of saying, 'I love you,' they say, 'Here, have a cookie,' " Robbins said.