Below are two basic examples of this contrast. The term refers to both the physical and non-physical aspects of focus, among other things. In this article, I am refering only to the physical side of this focus, particularly the idea of muscular tension timing. Although many are tempted to put a lot of tension in their upper arm at the moment the punching arm begins to move from its starting position, there is little need for such tension at that point. In fact, it will slow you down if you put too much tension into the arm early in its execution.
Tension slows the speed that the muscles move.
Imagine what happens to water when the temperature suddenly drops. Ice is hard, but it does not move quickly. Try to keep your upper body flowing, like the liquid state of the water, at least up until the moment of impact. Put only enough tension in the muscles of the arms, chest and back to get the arms to move in their proper courses. At the final instant, tense all the muscles of the body that you can.