Work out a way to stay in shape (4,3)
I believe the answer is:
keep fit
'stay in shape' is the definition.
(I've seen this in another clue)
'work out a way' is the wordplay.
'work out' becomes 'keep' (I can't explain this - if you can you should give a lot more credence to this answer).
'a way' becomes 'fit' (fit is a kind of way).
'keep'+'fit'='KEEP-FIT'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for keep fit that I've seen before include "Do physical exercises?" , "Maintain health" , "sort of exercise" , "Callisthenics" , "Exercise designed for physical wellbeing" .)