The saying in anatomy is that

"form follows function"

If you do a large amount of exercise and weight training you increase the size of your muscles and also the bones into which the muscles insert. There is a limit to this size increase. Often the important change is the muscle definition as with body builders.

High performance athletes usually work at, on, near or beyond the edge of what the body can do.

Athletes work very hard to enable their mind to rule their body, "Mind over matter". They often say that "If it doesn't hurt your not trying".