what are power and percision grips?

This is the two distinctive ways that hominids can manipulate their environment. Power grip is the way you would grab a barbell to lift it or the way you would grab the hilt of a heavy sword to swing it. The Precision grip is the way you would hold a pencil or pen. You will notice that if you put a pencil in your hand and hold it in a power grip you don't have much in the way of manual dexterity. The interesting thing about these grips, is that humans have a unique ability to do both at the same time. You can use a power grip in one hand and a precision grip in the other. This is probably what allowed us to develop tool making as we were evolving.