We learn from experience that certain physical actions and movement can be tiring if we repeat them as if we were purely mechanical objects. But we eventually learn how to do repetitive tasks in a way that lets us endure and prevent strain. The key to better sounding music and greater endurance is a combination of transferring weight and making a deal with gravity. For a simple comparison we can walk long distances without getting tired. What if you march the same distance? You would need to raise your legs higher and would find yourself getting tired much quicker. The fingers are the same. We can use our fingers, hands, wrists and arms and even body to affect the way we play. The role we give to gravity is important. If we let our fingers transfer the weight of our arms we are dealing with a predictable factor. Our arm weight is constant. We can play smoothly. If we want legato, that is playing without space or silence between each note then transferring weight is both efficient and effective. When Newton discovered gravity the amazing realization was not simply that the forces were there but that the movement of objects could be predicted and manipulated in a consistent manner. Remember hand position , finger curvature and providing the correct amount of opposing force to get the sound you need. For example: The melody is usually in the right hand. Then that would mean that more sound is required in the right hand so let gravity do the work by simply transferring the weight. But the left hand is an accompaniment. So, let the arm muscles provide a steady opposing energy up so that the left hand sounds quieter.