Like any true celebrity, Uggie, the Jack Russell terrier from The Artist and Water for Elephant s, puts in his time on the treadmill.

At 10, Uggie doesn’t do a heavy workout, just a light trot and walking, said owner-trainer Omar Von Muller of Los Angeles. But Von Muller bought Uggie a DogPacer for those times when he can’t go out.

"It’s important to keep him in shape," Von Muller said. "If they don’t get their exercise, they get old too fast, just like people."

Some 3 million dogs across the country were using treadmills in 2010, according to a survey of pet owners by the American Pet Products Association. The group asked about treadmills for the first time because the machines were selling so briskly, APPA President Bob Vetere said.

Heather Chau borrowed a DogPacer when her rescue dog Heidi arrived weighing 115 pounds. Heidi is now down to 80 pounds, and Chau, a Las Vegas bookkeeper, was so impressed, she returned the donated DogPacer and bought her own. Now all four of her dogs use it.

"I want to make sure the rest of their lives are the healthiest we can make them,” Chau said.

Treadmills come in a range of sizes and prices, from $499 for a low-end DogPacer to $3,000 for Jog A Dog.

The most visible difference between human canine treadmills is the size, because a dog’s stride is longer and his body shorter than a human’s, said David Ezra, the owner of Las Vegas-based DogPacer.

The company plans to release a treadmill for toy dogs in September, he said, and the price will be smaller too.