It hurts when I bend my knee.

我的膝盖一弯就疼。

《牛津词典》

Bend the front knee, keeping the back leg straight, press the right heel down on the floor.

前腿膝关节弯曲，后腿保持绷直状态，右脚后跟贴紧地面并向下压。

youdao

Bend the supporting knee during these transitions.

在这些体式变换时弯曲支撑腿的膝盖。

youdao

It is most unlikely to bend the knee.

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But Mr Khan refused to bend the knee.

ECONOMIST: Banyan

"Bend your left knee!"

WSJ: One Kid's Personal Tennis Academy