bend your knees

[stephenlearner]

Hi,

Why do people say "bend your knees"? I think they should say "bend your legs", because knees are joints. We bend a straight thing, don't we?

 

[grassy]

because knees are joints

And that's why we can bend them. You won't be able to bend your thigh or your shinbone.

 

[bibliolept]

The most correct way would arguably be "bend at the knees," but "bend your knees" is perfectly understandable and idiomatic in AE. the same is true for "bend your elbow" and "bend your waist."
,

 

[london calling]

And that's why we can bend them. You won't be able to bend your thigh or your shinbone.

Exactly.

 

[Edinburgher]

We do entertain the concept of the joint itself being straight or bent, depending on whether the angle between the bits that stick out is 180 degrees or not.