By DOUGLAS QUENQUA

A man’s best friend is not always his best choice of a running partner.

It’s a lesson that Michelle Powe, an English teacher in Midlothian, Texas, learned last summer when trying to run with Mookie, her 40-kilo Catahoula.

“He kept trying to herd me,” she recalled. For the entire 5-kilometer run, Mookie displayed the kind of herding behavior that is typical for the breed, throwing his weight against Ms. Powe and nipping at her legs.

“By the end of it, my knees were sore from having 90 pounds constantly bumping into me,” she said.

Not all dogs are born to run, particularly the way humans go about it: in a straight line, with little regard for scent. And there is nothing fun about running with an untrained dog. Indeed, it can be dangerous for both you and your pet.

“Invariably active dog owners wake up one day and say, ‘Today is a beautiful day, I’m going to go run with Fluffy,’ and they’ve never run with Fluffy before, and they set off and realize it really stinks running with Fluffy,” said Alexandra Powe Allred, a Dallas-based trainer (and Michelle Powe’s sister).

The first step for anyone thinking about running with a dog is researching the breed, Ms. Allred said. Some of it is common sense: small dogs will have trouble running at high speeds or for long distances.

But other problems may not be so obvious. For example, dogs with flat noses - pugs, bulldogs, some boxers - may have trouble breathing during strenuous exercise. And while some hunting or herding dogs are physically built for running - like border collies and Rhodesian Ridgebacks - they may be more interested in chasing prey than staying on the sidewalk.

Trainers say that if you teach your dog only one command before running, it should be “heel.”

Regardless of breed or training, all dogs display one trait that makes them appealing partners to runners who don’t like a lot of chatter: they don’t talk. But that silence also means you have to work harder to know when they are hurt.

“Dogs love their owners and want to be with them so much that they’ll just take whatever punishment you give them,” Ms. Allred said. “Sadly, a lot of these owners don’t think about it until they’re home and they realize, ‘God, what have I done to my dog?’ ”

The most common problem is overheating, said Teoti Anderson, former president of the Association of Pet Dog Trainers. “You’re going to see the dog’s tongue hanging out, and it will be round at the bottom” if the animal is getting too hot,

Ms. Anderson said. “Also you will hear some whining, and they’re going to start slowing down.” Ms. Anderson recommends taking your dog to the veterinarian before running together to make sure it is healthy enough. She also says never run with a dog younger than a year old (2 years for larger dogs, which take longer to mature).