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health advisory Hospital Doctor Yu 2007-11-8 19:09:42

you know how when you hold your arms at your side, they naturally have a slight bend at the elbow?

i don't think it's because of the extra leverage you get from your biceps, although you'd be able to get your hands up quicker to protect your head with the bend.

i think it's because you can run faster and if you didn't have the natural bend, you'd extend your arms fully behind you which would convert forward momentum backwards (instead of converting forward momentum to upward momentum as the bend in your arm does).

any thoughts?

Answers:

That's certainly possible. However, it doesn't have to be anything that specific. Your arm has to both extend and contract, and has muscles for both. In the extended position, the extensor is contracted, and it requires energy to keep muscles contracted. So the arm rests at a position where both the extensors and contractors can be suitably relaxed.

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Evolutionarily speaking, there's no competitive advantage for them to extend perfectly down in a relaxed position.

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I think you have too much free time. That is a thought.

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Well, consider this: higher tension means more possibility of breakage.

So, perhaps ther IS an evolutionary advantage to having your arms relaxed and not rigid?

If your arms and muscles are rigid, and somethign hits you with a lot of force, the tension means that extra energy put into the system might start snapping things. Whereas if there's elasticity, perhaps more of the impact will be absorbed and dissipated harmlessly. Consider a taut line and limp line. Pull them both up lightly with a knife. The taut line may well snap. The limp line will simply rise and maybe stretch a bit.