A few days ago there was a clue which tickled me when I discovered its solution - I did not solve it - so perhaps if you didn't see it or if you have forgotten it, it might please you.
24ac. Capital return or 1 across (5).
The clue for 1 across, should that be of any use, which I am not promising, was: Arm extension from this movement, note (7)
The answer to 1 ac was triceps