1- Play tug-of-war. Pulling for extended periods of time on a rope toy can seriously build up a dog’s leg and shoulder muscles. Of course, you need to be careful not to lift the dog off the floor while you are playing as this can hurt his back and teeth.
2- Fetch uphill. If your dog loves to retrieve, then indulge him. However, throw the balls up a hill so that he has to get a workout in to get them. Daily uphill fetching gets you quality time with your dog and will build up his muscle strength and bulk in no time.
3- Have play dates. Romping with other dogs is a great full-body workout for your dog. Make sure that the dogs are about the same size to ensure that no one gets hurt if the playing gets particularly physical.
4- Take your dog for a bike ride. You may have to practice to get this one down. You can take your dog for a leisurely bike ride by holding the leash and allowing him to run alongside the bike. You should start out going less than a mile, and never exceed more than three. Also, always let your dog set the pace. It is great cardiovascular exercise, and the prolonged running will quickly help build leg and shoulder muscle.
5- Encourage jumping. While you do not want your dog to jump on you, jumping over things can build muscle and enhance agility. You can take your dog on a run around the yard and encourage him to jump over logs and rocks, or you can build a jumping course out of tires or low hurdles. Do not try to get your dog to jump more than about a foot off the ground unless he has been trained.