Sluggish? Teach girl exercises (9)
I believe the answer is:
lethargic
'sluggish?' is the definition.
(similar in meaning)
'teach girl exercises' is the wordplay.
'exercises' is an anagram indicator (I've seen 'exercising' mean this).
'teach'+'girl'='teachgirl'
'teachgirl' with letters rearranged gives 'LETHARGIC'.
(Other definitions for lethargic that I've seen before include "lack of energy" , "somewhat slow" , "reluctant to move" , "Unenergetic" , "Lacking energy/enthusiasm" .)