Forcing learners to keep up exercise in Advent (10)
I believe the answer is:
compelling
'forcing' is the definition.
'learners to keep up exercise in advent' is the wordplay.
'learners' becomes 'll' (I've seen this in other clues).
'to keep up' is a charade indicator (letters next to each other) (in a down clue, some letters go beneath others).
'exercise' becomes 'pe' (Physical Education).
'in' indicates putting letters inside.
'advent' becomes 'coming' (synonyms).
'll' put after 'pe' is 'pell'.
'pell' going inside 'coming' is 'COMPELLING'.
(Other definitions for compelling that I've seen before include "Making" , "Driver's action" , "arousing strong interest" .)