Focusing on muscles and isolated movements is mentally convenient. It is very easy to break the body and movements into parts and separate systems and focus on thus parts to the exclusion of the whole. It may be convenient and easy but is not right, it ultimately leads to confusion.
The body moves and works through connections, chain reactions and synergies. The brain does not recognize individual muscles, it recognizes patterns of muscle synergies. To optimally prepare the body for the stresses of competition you must focus on enhancing those connections and synergies. Give the body credit for what it can do, it is smart, so coach it smart. Good coaching is giving the body increasingly complex movement problems to solve by putting the body in positions to solve those problems.