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Can you bend your thumb backwards until it touches your wrist?
你是否能將大拇指向后彎曲直至其觸碰到手腕部位？
If you join your hands behind your back, can you lift them over your head without letting go?
你將雙手在背后緊握，是否能夠?qū)⑵渑e過頭頂而不松手？
If you can, you might be what some people call double-jointed.
如果你能做到，那么你可能擁有雙關(guān)節(jié)。
But, A Moment of Science wonders, how could anyone have double joints?
但是，《科學(xué)一刻》想知道，一個人怎么可能擁有雙關(guān)節(jié)呢？
Double-jointed people don't really have two joints.
所謂雙關(guān)節(jié)的人并非真正擁有兩個關(guān)節(jié)。
Any joint, such as the thumb joint or the shoulder, can be called double-jointed if the tendons and ligaments surrounding the joint allow a wider range of motion than is usual.
任何關(guān)節(jié)，如肩關(guān)節(jié)或拇指關(guān)節(jié)，若圍繞其四周的韌帶和肌腱的活動范圍超出平常，則可被稱為雙關(guān)節(jié)。
Joints are created whenever 2 adjacent bones meet.
關(guān)節(jié)是兩骨相接而形成的。
They have fibrous bands of connective tissue called ligaments that stabilize the joint.
他們含有被稱為韌帶的結(jié)締組織纖維帶，韌帶能夠穩(wěn)定關(guān)節(jié)。
Connective tissues also form the tendons that join the bones to the muscles.
結(jié)締組織同時也組成了連接肌肉與骨頭的肌腱。
Ligaments and tendons usually restrict the movement of the joint, but in some people, these normally restrictive tissues can be quite flexible and allow the extra movement we call double-jointed.
韌帶與肌腱通常會限制關(guān)節(jié)的活動，但是對于某些人來說，這些結(jié)締組織非常靈活，能做出更大范圍的運動，也就是我們所稱的雙關(guān)節(jié)。
Practice can increase a joint's natural flexibility just the way stretching can increase your muscles'flexibility.
通過鍛煉能增加關(guān)節(jié)的自然柔韌性，正如伸展運動可加強肌肉的柔韌性一樣。
While flexible joints are very useful to contortionists, some joints can become so loose that they are unstable.
靈活的關(guān)節(jié)對柔術(shù)演員來說至關(guān)重要，但他們的一些關(guān)節(jié)可能會變得十分不穩(wěn)固。
This allows the bones of the joint to slip out of their sockets and can be very damaging.
這很容易造成關(guān)節(jié)脫臼，對身體造成很大的傷害。
Strengthening the muscles around the joint can stabilize it and still allow you to show off your trick joint at parties.
加強關(guān)節(jié)周圍肌肉的鍛煉能夠使關(guān)節(jié)穩(wěn)固，并且你依然可以在各式派對上炫耀你的小把戲。
