It’s some cheek saying America trails EU in surpluses (7,7)

I believe the answer is:

gluteus maximus

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

'it's some' is the definition.
I can't judge whether this definition defines the answer.

'cheek saying america trails eu in surpluses' is the wordplay.
'cheek saying' becomes 'maxim' (maxim is a kind of saying. I am not sure about the 'cheek' bit.).
'america' becomes 'US' (United States).
'trails' is a charade indicator (letters next to each other) (some letters follow or trail others).
'in' means one lot of letters goes inside another.
'surpluses' becomes 'gluts' (I've seen this in another clue).
'eu' placed inside 'gluts' is 'gluteus'.
'maxim'+'us'='maximus'
'maximus' put after 'gluteus' is 'GLUTEUS MAXIMUS'.

Can you help me to learn more?

(Another definition for gluteus maximus that I've seen is " behind in Latin".)

I've seen this clue in The Sunday Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.