The quadriceps straightens the back knee.

股四头肌使后腿膝盖伸直。

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Keep your front shin vertical, back knee straight, back heel lifted, and chest lifted.

保持前面小腿垂直地板，后膝伸直，后脚跟离地，胸腔上展。

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Don't allow back knee to touch the ground and keep hip, knee and ankle aligned facing forwards.

后膝不应接触地面，并保持髋关节，膝盖和脚踝正面朝前对齐。

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Mr.Heppner had his own leg tied back so that a wooden leg could be attached at the knee.

VOA: special.2010.06.11

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