Technique set up to restrict pain in part of body (7)
I believe the answer is:
trachea
'part of body' is the definition.
('trachea' is part of 'body')
'technique set up to restrict pain' is the wordplay.
'technique' becomes 'art' (I've seen this in other clues).
'set up' says the letters should be written backwards.
'to restrict' is an insertion indicator.
'pain' becomes 'ache' (ache is a kind of pain**).
'art' backwards is 'tra'.
'tra' placed around 'ache' is 'TRACHEA'.
'in' acts as a link.
(Other definitions for trachea that I've seen before include "airy passage" , "airway" , "body part" , "Tube taking inhaled air from the larynx" , "where air passes" .)