Exercises for body and soul? Unknown in the past, going back (4)
I believe the answer is:
yoga
'exercises' is the definition.
(I have seen 'Healthy exercises' mean 'yoga' so perhaps 'exercises' could also mean 'yoga')
'unknown in the past going back' is the wordplay.
'unknown' becomes 'y' (algebra).
'in the past' becomes 'ago' (three years ago means three years in the past).
'going back' shows that the letters should be reversed in order.
'ago' written backwards gives 'oga'.
'y'+'oga'='YOGA'
'for body and soul?' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for yoga that I've seen before include "Healthy exercises" , "Hindu philosophy involving mental and physical exercise" , "(Hindu) mind and body toning" , "path to enlightenment" , "E.g. Lotus position" .)