One brief moment to take in a certain type of exercise (9)
I believe the answer is:
isometric
'one brief moment to take in a certain type of exercise' is the definition.
I can't judge whether this definition defines the answer.
'one brief moment to take in a certain type of' is the wordplay.
'one' becomes 'i' (Roman numeral).
'brief' means to remove the last letter (a shorter or briefer version of the word).
'moment' becomes 'trice' (I've seen this before).
'to' means one lot of letters go next to another (I've seen this in other clues).
'take in a certain type of' becomes 'some' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'trice' with its final letter taken off is 'tric'.
'tric' after 'some' is 'sometric'.
'i'+'sometric'='ISOMETRIC'
Can you help me to learn more?
(Other definitions for isometric that I've seen before include "Type of angled drawing to scale - eroticism (anag)" , "equal in measurement" , "Having equal dimensions" , "Like some exercises" , "of equal size" .)