The bottom line is, and will always be GENETICS.
Genetic response to TRAINING
Genetic response to NUTRITION
Genetic response to DRUGS
It can be all of the above, or some of the above.
Boatloads of drugs? Think again...You probably could not handle the amounts that a genetically gifted person can.
Why is it that some people can smoke, drink, abuse their bodies and never have an issue? Genetics is why!