Exercise isn’t just a nicety; it’s a necessity for maintaining optimal physical and mental well-being. As with people, obesity is becoming a major health problem in today’s dogs. Between 20 and 40 percent of all dogs seen by veterinarians in the United States are considered overweight, and many are clinically obese. Obesity prevents dogs from enjoying many physical activities; it also decreases speed and stamina and makes it more difficult for dogs to deal with heat. Obesity is also associated with certain medical problems, including arthritic changes in overly burdened joints, increased risk of torn ligaments, back problems, cardiac problems, difficulty breathing, increased surgical risks, skin problems, whelping problems and a possible increase in risk for some cancers.

      If the physical threats associated with obesity aren’t enough, consider the behavioral aspects of a lack of exercise. Dogs are active by nature. Their ancestors, wolves, covered many miles every day in search of food. Many domestic dogs were selectively bred to be even more active, with a focus on hunting or herding or patrolling. Preventing them from their genetically programmed activity level can build frustration, which may exhibit itself in the form of hyperactivity, barking, digging, tail chasing, and home destruction. Boredom has also been associated with behavioral problems in some dogs.

     Don’t think you can just stick your dog in the yard and trust him to exercise himself. Unless he has a friend in the yard with him or lots of stimulation on the other side of the fence (in which case he’s probably barking too much to be a good neighbor), he may chase his tail a few times, sniff around, and then just sit there. You’ll need to play coach to get him in shape….read more at http://www.vetstreet.com/our-pet-experts/your-dog-why-exercise-is-important