Sometimes you might blow off walking your dog. But do this too much, and your dog suffers–more than you know. You do too whether you realize it or not. Check out this great article by Christie Keith on the Pet Connection Blog about
“What you lose when you can’t walk your dogs”

It’s 20 degrees, the wind’s kicked up, and the sun just set. I don’t care how sad my dog looks, a walk this evening is out of the question. Even if I wanted to brave it, it is dangerous for him, even with dog boots and a dog coat. But we need to do something.
If [...]

Often lack of exercise is not the dog’s fault.
No diet, however superior will provide the kind of health necessary to live a long life without adequate daily exercise. He may be kept inside all day while you are out, and there is only so much activity he can do at home alone. In any case, [...]

The veterinarian told the not-so-bright guy that his dog needed some exercise. 
“You need to make sure this dog runs around,” the doctor said. “Try playing a game of fetch with him.”
“I can’t play fetch with my dog,” the doofus said.
“Why not?” the doctor asked.
“Because,” he replied, “He can’t throw.