Man's best friend makes a loving and loyal pet—and an awesome fitness partner. With all the walking, chasing, and playing you do together, keeping up with your dog can be an exercise in and of itself. Case in point: dog owners walk more than those without a pooch, averaging four walks a week for 160 minutes of physical activity, according to a study published in the Journal of Physical Activity & Health. You'll boost your fitness by owning any dog, but breeds with extra stamina and agility will really keep you moving. Whether you like to run, swim, hike, or play games in your yard, these ultra-active breeds will help you stay in shape.