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So some people can’t crack their knuckles.Can you, Rob?
所以有些人是不会掰指关节的。你会吗，罗伯？
I don’t know, and I’m not about to try.But it isn’t just finger knuckles that crack – you can do it with your neck, back, knees, ankles and toes.
你会吗，罗伯？不仅是指关节可以掰响，脖子，后背，膝关节，脚踝，脚趾都可以。
Professor Greg Kawchuk says that comparing people who crack their knuckles and people who don’t might provide some insight – or understanding – into whose joints are healthier.
Greg Kawchuk教授表示，仅凭是能否掰响指关节，无法看出谁的关节更健康。
Sounds interesting.But what actually happens when you crack your knuckles, Neil?
听上去很有意思。但是当你掰响指关节时，到底会发生什么？
Well, when you stretch or bend your finger to pop the knuckle, you’re making the bones of the joint pull apart… like this…(cracking knuckles)
当你伸展或弯曲手指，掰响指关节，就使得关节处的骨头撕裂开，就像这样（掰响指关节的声音）。
Please don’t do it again!
拜托别这样了。
Well, it stretches the space around the joint and surrounding fluid and causes a decrease in pressure.As a result, gas dissolved in the fluid becomes less soluble – or less able to be dissolved – leading to the formation of bubbles.Now when you stretch the joint far enough, these bubbles burst, producing the ‘pop’ sound.
掰响指关节时，关节和周围滑液的空间拉大，压力减小。最终溶解在滑液中的气体愈发不溶于液体，产生微小的气泡。当你尽可能的伸展关节时，这些气泡破裂，发出“砰”的响声。
Ouch! Excellent – well, thanks for the biology demonstration there, Neil …
太奇妙了，多谢你这专业的生物学解释。
Any time! Any time, Rob!Now let’s hear from the professor again about the medical value of research into knuckle cracking.
不用谢，不用谢。我们再来听听教授对掰响指关节研究的医学价值的看法。
When our engineering colleagues do this between two flat surfaces say of ceramic or porcelain… When they do this and they pull them apart quickly and there’s a little bit of fluid in betweenthey can use electron microscopy to see there’s been tremendous damage to the surfaces of the joints.But for some reason we don’t see that in the human joint.There’s something that makes it very resilient.
我的同事用两个陶瓷平面来模拟这一现象，平面中间还有一些液体，他们快速的将两个平面分开，然后使用电子显微镜来观察这对关节平面造成的巨大损害。但是不知道基于什么原因我们未能在人类关节上看到这一点。有什么东西让关节变得很有弹性。
Interesting stuff!So scientists have performed experiments to imitate what happens in a human joint when you crack your knuckles.And when you quickly pull apart a pair of ceramic – or clay – tiles with fluid between them, it causes a lot of damage to the surface of the tiles.

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