The skeleton you are bequeathed with, David Epstein explains (in The Sports Gene), has a lot to do with whether you will ever pack on the weight you need for a particular sport:
In measurements of thousands of elite athletes from soccer to weight lifting, wrestling, boxing, judo, rugby, and more, Holway has found that each kilogram (2.2 pounds) of bone supports a maximum of five kilograms (11 pounds) of muscle. Five-to-one, then, is a general limit of the human muscle bookcase.
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Male Olympic strength athletes whom Holway has measured, like discus throwers and shot putters, have skeletons that are only about 6.5 pounds heavier than those of average men, but that translates to more than 30 pounds of extra muscle that they can carry with the proper training.
Training builds bone, muscle, and tendon. The bones in a pitcher’s throwing arm are much denser than in his catching arm.
Steroids only build muscle, so roiders sometimes flex their muscles hard enough to break bones and tear off tendons.