In good shape, after going up rocky island (4)
I believe the answer is:
elba
'island' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for elba that I've seen before include "Able was I ere I saw ... (palindrome)" , "Napoleon's Mediterranean exile island" , "part of Tuscany?" , "Island of Napoleon's first exile" , "Napoleon's prison isle" .)