For the stair climbing and descending activities the PF reaction
force attained a level of 3.3 body weight. This value is almost seven
times the PF joint reaction force obtained during level walking. This
figure gives the explanation why the patients with patello-femoral
joint derangements experience more pain while climbing and descending
stairs. Patients with PF joint derangements adapt their gait pattern
in stair walking by assisting with the uninvolved side in order to
decrease the muscle force. The push-off with the unaffected leg
helps considerably in decreasing the muscle force when climbing stairs.