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It's hard, running along the motorway! (8)

Ross

I believe the answer is:

shoulder

I'm a little stuck... Click here to teach me more about this clue!

'motorway' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I can't see?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for shoulder that I've seen before include "Joint - ours held (anag)" , "On the side of the road, it might be hard" , "Part of the body (that bears burdens?)" , "Undertake (burden)" , "See 10" .)

I've seen this clue in The Guardian.
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