@Zkaiser:
His heart and organs have the physical properties of rubber.
Yeah. Cool. Thats why his heart doesn't explode to pieces when he pumps his blood through his body.
But the whole body works like any other body. Biologically and chemically… well, i guess you know what happens if you try to "dope" your body beyond the limits..... the organs will be damaged (muscles for example); Ever thought about the amount of air he needs to consume in order to get a hold on his higher oxygen-consumption?
Thats the stuff graveyards are filled with...
Edit: Letting the body generate more energy will always result in chemically damaged organs. Or another example: Lets say you are a good runner, but if you stress your leg muscles too much and in a wrong way, you can end up in a wheelchair just by running, without any accidents.
If you don't use your body in a proper way, it will fall apart.