Picking your dog up by his limbs, such as lifting him by the front legs, can cause serious injuries. Picking him up by the middle is a little safer, but it can still be uncomfortable if all of his weight is supported by his belly over your arm or only one hand.
To avoid injuries, you shouldn't lift your dog only by the middle. If he is small, or under about 20 pounds, place one arm around the dog with your hand under his ribcage, just behind his front legs. Place the other hand at the base of his neck where it joins with the front of his chest so that his weight is distributed between both hands. If your dog is larger, place one arm around him so that your hand is under his lower abdomen, just in front of his rear legs, and the other hand on the front of his chest just below his neck. You can pick up a large dog by placing one arm under his rump, instead of his lower abdomen, so that he is almost sitting on one arm while the other supports his chest and neck.