Watching the NFL (ie, real football for non-Americans) draft last weekend, they would often mention some prospect "has a good bubble". I didn't know exactly what they were talking about, but got confirmation on the radio today. It means they have a good--big--butt. As the gluteus maximus, or buttock muscle, is the largest muscle in the human body, it is useful signal of overall musculature.

Just an FYI.