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Comment by mirkules | Hacker News Reader

I've heard that too: in the event of an accident, it's better to relax all muscles than to tense them up (particularly, I've heard this about whiplash). Why is that?

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When taking a big fall rock climbing the advice is to relax, enjoy the fall and shout something. Animal noises are the most fun, expletives the most common. The shouting is to make sure you're breathing out as you fall onto your harness rather than breathing in, and to give you something to concentrate on so you don't tense up in fear.

I'm not really sure why it helps, but I can certainly say it does. I know that when I panic and go stiff it hurts more as my tense body hits the rock. Even when in a similar mental state, hitting the rock with a relaxed body is less painful.

My understanding is that when tense, you're more likely to resist the way your body is going to move, causing more injury. The forces involve are such that you can't actually make a significant change in where you're going to go, but if you tense up you may end up putting a lot of force in a little area. Like, say, you tense up your leg, which puts all of the force into your knee or ankle.

Anecdotal evidence: My dad (around 50 years old) still has periodic pains in his hip from an accident 20-25 years ago because he tensed his legs, making them rigid and sending the force of the collision through his bones, shattering fragments inside his hip. To this day he still has minor bone fragments in his hip which presumably cause the pain.

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