Do this and take notice? (3,2)

I think it could be either:

Which length description are you looking for?:

3,2

sit up

(Other definitions for sit up that I've seen before include "It takes physical effort" , "Suddenly show interest in" , "postpone retirement" , "Pay attention - . . . . . and take notice" , "may aid fitness" .)

I've seen this clue in The Guardian.

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.