Key worker is involved in exercise after Tuesday's vacation (6)
I believe the answer is:
typist
'key worker' is the definition.
(I've seen this before)
'is involved in exercise after tuesday's vacation' is the wordplay.
'involved in' is an insertion indicator.
'exercise' becomes 'pt' (Physical Training).
'after' is a charade indicator (letters next to each other).
'vacation' suggests removing the centre (middle letters vacate the word).
'tuesday' with its middle removed is 'ty'.
'is' going into 'pt' is 'pist'.
'pist' after 'ty' is 'TYPIST'.
(Other definitions for typist that I've seen before include "Someone paid to copy using a keyboard" , "Pre-computer office worker" , "Old secretary" , "Operator of a machine that prints one character at a time" , "Skilled keyboarder" .)