Spongy muscle needs at first to be covered in ice (9)
I believe the answer is:
absorbent
'spongy' is the definition.
(similar in meaning)
'muscle needs at first to be covered in ice' is the wordplay.
'muscle' becomes 'ab' (short for abdominal muscle).
'at first' says to take the initial letters.
'to be covered in' is an insertion indicator.
'ice' becomes 'sorbet' (sorbet is a kind of ice).
The first letter of 'needs' is 'n'.
'n' going inside 'sorbet' is 'sorbent'.
'ab'+'sorbent'='ABSORBENT'
(Other definitions for absorbent that I've seen before include "able to soak in the sun?" , "Bob ran set (anag.)" , "Like a towel" , "taking everything in?" , "Able to soak up moisture" .)