Sort of exercise drill in CIA gets backing (7)
I believe the answer is:
aerobic
'sort of exercise' is the definition.
'drill in cia gets backing' is the wordplay.
'drill' becomes 'bore' (synonyms).
'in' indicates putting letters inside.
'gets backing' shows that the letters should be reversed in order.
'bore' put into 'cia' is 'ciborea'.
'ciborea' back-to-front is 'AEROBIC'.
(Other definitions for aerobic that I've seen before include "(Of exercises) related to increasing oxygen in blood" , "Of a process depending on oxygen" , "Like exercise that aids the intake of oxygen" , "Exercises to enhance respiratory efficiency" , "Exercise to improve cardiovascular health" .)