In-Game Explanation for Body Points?

When someone purchases body points, what's really going on physiologically?

Say someone has 5, someone else has 30, and a third person has 90? What does that represent?

It could be anything from narrowly dodging, glancing blows, physical toughness, supernatural toughness, or perhaps something else.
It has been, and currently is, up to the player to think about how they see it.