Acquiescing obediently, though disheartened, while performing inversion during exercise (4)
I believe the answer is:
yoga
'exercise' is the definition.
(I know that yoga is a type of exercise)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for yoga that I've seen before include "(Hindu) mind and body toning" , "Hindu physical and mental exercises" , "System of exercises for bodily or mental control" , "E.g. Lotus position" , "Hindu body work" .)