system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why during a car crash or any accident do we get hurt more from having our muscles tense? Don't we tense up to protect ourselves?
gpt
You tense up ready to react if you have to. It's not an advantage in an impact but for most of our evolution, we weren't in much danger of high speed impact unless you fell out of a tree or off a cliff.   

There were far more situations where being poised to suddenly spring into action was more likely to save your life.