Answer:
adrenaline and a stressful situation.
Step-by-step explanation:
in your everyday life, your brain holds back most of your strength as to stop you from hurting yourself. in stressful situations, your brain lets go and allows you that strength and releases adrenaline in order to give you the energy to use that immense, superhumanly strength, in order to achieve its goal, your survival. this is a simplified answer but it's what I can give you. I'd suggest skimming the article in case they touch on other topics and information.