Consider Einstein's famous equation, E = mc2. If E and m are the energy and mass of an object (depending on what the object is), and c is the speed of light, which letter represents a constant?
Light, unlike us, doesn't become tired and slow to a near crawl after ever quarter lap. The speed of light never changes, so c is a constant. But E and m, on the other hand, are variables since they change depending on the object. In other words, the greater an object's mass, the greater the amount of energy. Taking your gargantuan, couch-dwelling Uncle Leroy into consideration, this information is actually hard to believe.