I guess I have to clarify the hill work.....hill work is recommended for strengthening muscles especially in the hindquarters of horses with upward fixation of the patella. Also steady trot work, again, to build muscle.
If other stifle or hip problems are present I agree hill work can become a problem.
To stay on the safe side, I would walk hills in hand and trot and longe on the flat
Important is trot for building muscles, not jog.Freshly forward trot.