Get a Vet Checkup
"Take them in for a quick vet exam and have basic blood work done; see if they have heartworm or a heart murmur," says Woodard, both of which could affect the dog's ability to be active. You'll also want the vet to give you a recommendation for safely ramping up the dog's activity level. "If the dog is already underweight, you don't want them to lose more weight," she says, adding that you need to be especially careful if you're adopting an underweight small dog. A four-mile run may seem like nothing to you, but it's a long ways if your legs are only six inches long.