I can only imagine the difficulties with running that you face. We normally recommend people substitute hiking for running when that can’t run. You can certainly use the assault bike for some of your aerobic workouts. However, bear in mind that this event, Elbrus is going to require you to hike many hours up and down hill. As much as possible you should try mimic the demands of the climb itself. If you have access to a stair machine, stairs in a tall building or actual mountain terrain these will all give better results.