Now a more challenging question; what do you do about it? All dogs need to do more than eat, sleep and love you. All dogs need exercise to start with. A walk isn't just about having a pee or a poop. A walk is a fabulous way to build a strong bond between you and your dog, and an opportunity to demonstrate to your pet that YOU are the leader. As Cesar Millan, the dog whisperer, would say, "YOU need to be the Pack Leader". Remember that when you walk your dog, you should be the first one out of the house, the first one back into the house, and your dog should walk beside you or slightly behind you.
I know that we all love our dogs and often think of them as our children... our babies. Truth be told, in order to provide your pet with what he/she truly needs it is important that you think of your dog first as a dog, and then consider the characteristics of the breed. Then you need to remember that your pet is also an individual.
On the other side of the spectrum; Poodles, Terriers, Shih Tzus, Schnauzers, Bull Dogs, and Pugs, for example have a much lower demand for exercise. Understand that these dogs still need to be walked, at least once each day for at least one hour.
You'll know if your dog is getting enough exercise based on its' behaviour and weight. If your dog is gaining weight you're either feeding him way too much, offering too many treats, or not giving him enough exercise. If your dogs' weight is fine and he's behaving, then the exercise that you're giving him is likely sufficient. Remember, too, that older dogs will need less exercise than puppies. If there is any question or concern, get advice from your Vet.
One thing to note about walks is that you do NOT want the walk to be about your dogs' bathroom duties. Dogs absolutely LOVE their walks. If the walk is over immediately after the dog does his "business", he will try to hold it so the walk will last longer. In fact he may wait until you give up and go home, then do his business in the house. It will work better for you if you wait for the dog to "potty", and then reward that behaviour with a one hour walk.