My father put on five pounds the summer after our cocker spaniel, Budgie, died. Without the family pet's need for an after-dinner walk, Dad stopped taking his nightly, 45-minute stroll around the neighborhood. Within a few months, his waistline expanded.

I remembered this recently when I saw a friend who'd been trying to lose weight for years and discovered that he'd finally managed to shed 15 pounds. How?

"Got a dog," he said. "We walk three miles every morning."

Fitness experts regularly advise people to workout with a buddy because studies show that those who exercise with a partner are more likely to stick with their program. But while the research considers only human exercise pals, I'm certain the conclusions could extend to canine companions as well. Dogs provide wonderful camaraderie and motivation to be active, while adding an extra measure of safety and a huge serving of fun. And unlike a human workout buddy, your dog will never cancel on you at the last minute or bore you with obscure details of an intricate business deal.

Even regular exercisers can add a new dimension to their workouts with a dog. Although I've been hooked on my morning run for years, it's become even more fun in the year since our family got Sheba the Beagle. Sheba's shaken up my old routine--a 30-minute jog around the high school track--since she can't abide merely running in circles and refuses to wait patiently for me while I do. So now I tackle something I once hated. We run hills. Up and down our hilly neighborhood, Sheba and I run several miles, stopping frequently to sniff for squirrels (Sheba) and breathe deeply (me).