good starting point. question, what is the most problematic area in human motion, like walking? what would you say the amount of energy we expend to maintain stability? how much would such expenditure in energy for stability went force applied to your body? or when you apply force to something/someone? would stability important in martial context? so back to the example of picking up the spoon. the spoon exerted a downward force (gravity) onto me. i have to deal with such force by direct it to the ground (bring the ground to the spoon) by using mental intent to create a path from the spoon to the ground through my body, say from my right fingers, the ones i used to pick up the spoon, to my left foot. you will soon realize that there are areas in your body where muscles alone isn't enough for stability. what if someone replaced the spoon with a 10kg weight? would you need to change your posture to accomodate? internal folks would say no, because the same path would still be used and the same mental intent still applied.
I think Phi raises a good point here, which hopefully helps differentiate between the concept of efficiency between internal and external and what the goal of principle based training is.