Exercise builds muscle, burns fat, and strengthens the cardiopulmonary system. In addition, it staves off Alzheimer's disease in humans and, in all likelihood, has a similar brain-cell-sparing effect in offsetting the canine equivalent, canine cognitive dysfunction (see chapter 9).
It has been known since the turn of the twentieth century that the most important determinant of life span in animals is net caloric balance. If the caloric intake is in excess of output, fat will accumulate at a rate proportional to the imbalance. I'm reminded of Mr.Micawber's observation in Charles Dickens's David Copperfield: "If a man had twenty pounds a year for his income and spent nineteen pounds nineteen shillings and sixpence, he would be happy, but if he spent twenty pounds one he would be miserable."
Paraphrasing: Intake seven calories an hour (for a small dog), expenditure six calories an hour, result, weight gain and eventual misery. Carrying extra weight shortens dogs' health span and leaves them prone to various medical problems ranging from heart disease to orthopedic problems to cancer.
Obesity in our canine companions has reached the same epidemic proportions that it has in humans=and for similar reasons. Indeed, one in three dogs in the United States is overweight. There are three factors that affect body mass index (body mass index is weight adjusted for a physical size). The factors are: food intake, metabolic rate, and activity level. There's not much you can do about a dog's metabolic rate, unless he is hypothyroid, in which case thyroid hormone levels can be adjusted by hormone replacement therapy. That leaves two components, intake (food) and output (exercise), as malleable variables. Of course, on the intake side of the equation, it makes perfect sense to ration a dog's diet properly, but it is equally important to control the output side, which is exercise. All good weight-loss programs should address both sides of this equation. Dogs that are regularly exercised live up to 30 percent longer than their sedentary counterparts.
Okay, so let's say that at this point we agree that exercise is physically and mentally good for dogs. Should it therefore be a prescription for all dogs every day? The answer is yes, if at all possible. That said, some people have difficulty finding time to exercise their dogs, like the couple I mentioned earlier. In such cases a solution must be found, whether it is in the form of a paid dog walker (dog exerciser) or a few days a week at doggy daycare – which can really tucker dogs out.