diff --git a/Pose2Sim/Utilities/bodykin_from_mot_osim.py b/Pose2Sim/Utilities/bodykin_from_mot_osim.py
index 9c85a99..62140ba 100644
--- a/Pose2Sim/Utilities/bodykin_from_mot_osim.py
+++ b/Pose2Sim/Utilities/bodykin_from_mot_osim.py
@@ -123,8 +123,9 @@ def bodykin_from_mot_osim_func(*args):
                 model.getCoordinateSet().get(coord).setValue(state, motion_data_np[n,c], enforceContraints=False)
             except:
                 pass
-        model.assemble(state)
-        
+        # model.assemble(state)
+        model.realizePosition(state) # much faster (IK already done, no need to compute it again)
+           
         # Use state of model to get body coordinates in ground
         loc_rot_frame = []
         for b in bodies:
diff --git a/Pose2Sim/Utilities/trc_from_mot_osim.py b/Pose2Sim/Utilities/trc_from_mot_osim.py
index 359ff30..acf3e6a 100644
--- a/Pose2Sim/Utilities/trc_from_mot_osim.py
+++ b/Pose2Sim/Utilities/trc_from_mot_osim.py
@@ -81,7 +81,8 @@ def get_marker_positions(motion_data, model, in_degrees=True, marker_list=[]):
             else:
                 value = motion_data_pd.loc[n,coord]
             model.getCoordinateSet().get(coord).setValue(state,value, enforceContraints=False)
-        model.assemble(state)
+        # model.assemble(state)
+        model.realizePosition(state) # much faster (IK already done, no need to compute it again)
         # get marker positions
         marker_positions += [np.array([marker_set.get(mk_name).findLocationInFrame(state, model.getGround()).to_numpy() for mk_name in marker_set_names]).flatten()]
     marker_positions_pd = pd.DataFrame(marker_positions, columns=marker_set_names_xyz)