Canids have evolved as incredibly efficient predators. In the wild they cover many miles each day looking for food, sprint frequently to catch prey animals, wrestle and fight with each other, and mate. This combination of activities burns calories, develops cardiovascular ability, builds muscle, and maintains limberness.
Our job as stewards of domestic canids is to provide an exercise program that will accomplish all of the same health benefits. Of course this is challenging, especially since there are so many hazards in the world that getting your dog off leash to run while ensuring their safety can be extremely challenging.
Activities like walking are great, and should be done! But, they are only marginally useful as exercise. Exercise needs to either be elevating the heart-rate, or pushing muscles to fatigue, or stretching muscles. Most canids can be maintained in fairly good condition with 5-10 hours per week of strenuous exercise. Some options: