My own theory is that it takes a few years to develop the mind muscles connections, and for all the neglected muscles to be correctly worked and reach a whole body equilibrium. After that you know how to use the exact muscle group for a specific activity or movement, and every muscle is trained. Weight lifting or Yoga can both get to that, or any activity as long as you are mindful about movements and muscles involved, and every muscle is worked. It seems obvious but a lot of people don’t know and feel their muscles and their relative action when they do a movement like getting up or grabbing something.