Modern science tells us that the brain does not recognize individual activity...it doesn't need to. Instead the brain looks at movement patterns and creates coordination between all the muscles needed, this coordination is called a motor program. Muscle development does not play a major role in motor pattern development. Don't confuse form with function. Weight training with muscle isolation is popular in bodybuilding because bodybuilding is about form.
Muscle size and symmetry are the goals. But most sports are about movement. Speed,Quickness, Agility, Power, Control, Coordination and Stamina are keys to success.
The goal of training is not to change how the body looks, but to improve how the body moves. Therefore, sport or athletic training should focus on movement patterns rather than individual muscles.
Muscles will develop naturally as different movement patterns are worked, so most athletes will look as if they have done some bodybuilding. But the focus is on function, great form is just a by-product. Movement is ultimately what defines great athletes. It certainly is what defined Barry Sanders.
At 5 feet 8 inches and 203 pounds, Barry had a relatively average, if not small body for the NFL. Many wondered whether he could survive the punishment dealt out in professional football. But Barry's ability to move was unique. He was compact and quick. He demonstrated a perfect balance of control and quickness. He soon quieted his critics...but his physique didn't define his career, his movement did.
To be ignorant of motion is to be ignorant of nature.