She has been in at least three fitness programs. She runs on the treadmill. She swims in a lap pool. Her trainers shout encouragement. And although her target weight still eludes her, Lolita remains optimistic, smiling gamely during her workout and snacking on carrots.

If only her legs weren’t so short.

Lolita is a 4-year-old dachshund, a breed that like the beagle and Labrador retriever is prone to putting on extra pounds. In her case, about eight pounds too many.

But the problem of overweight dogs cuts across breeds. More than half of American dogs are overweight, according to the Association for Pet Obesity Prevention, an organization founded by a veterinarian to draw attention to the problem. And in dogs, as in people, extra weight is linked to diabetes, arthritis and high blood pressure as well as kidney and respiratory diseases.

Reducing calorie intake is part of the solution, veterinarians and pet behaviorists say. But diet without exercise isn’t enough. So dogs have been hitting the gym for fitness programs at kennels and pet spas around the country.