Walking up and down stairs, or running up and down stairs, for strengthening and conditioning for hiking and life in general, as well as rehab in some cases, even a few minutes walking slowly backwards on the treadmill works, if starting slow and using the sides for balance. Preparing someone for the ASCENT is all good and well but the DESCENT is the killer, ask any ultra distance runner of the comrades which is worse, the up or down run? the same can be said for hiking and tactical work, as well as rehabilitation.