Now, something I learned.
Hysterical strength
Adrenaline is our basic power up, it allows us to use more and more oxygen the more we have, and hardens our muscles to increase strength greatly, now something you might've not known, is the fact that with enough adrenaline, and a strong scenario, such as your child trapped under a car, you can gain so much strength from the rush at that given moment that you can lift that car off given person.
Another odd strength fact
Yelling does make you stronger. It's a proven fact that grunting, screaming, and producing any loud sound of rage will raise your adrenaline levels so high, that you can accomplish some pretty amazing feats in this hyped up state.