Samson's are awful Andrea. In his case it is from being chained up and laying on concrete for long periods of time. He has no hair on his elbows and very thick callouses. Angel doesn't seem to have any tho, least not yet.
Yes they are called elbow callouses. They are a result of pressure. It's to protect against the pressure of lying down on a firm surface. It's simply the thickening of the skin to protect it.
It's like a dog's foot pad, which should be thick. Some dogs have very thin foot pads and they get sore, while dogs that go for walks more often tend to have rough/thick pads. There are many ways to help "soften" the skin, but in reality if they are going to walk or lay on a hard surface you dont wan't to.