Step 6 - Extract forces and moments

Remember that joint reactions already contain the joint forces and moments as part of its components. We now need to transform each into the correct reference coordinate system, and possibly rearrange its order to conform to biomechanical conventions.

To extract joint forces:

1. Create a new variable called NormalizedLeftAnkleForces.
2. For the function type, specify Kinetics and for the function, select Extract forces from reaction A in segment B's reference, C normalize.

3. For the Input Variable type, select Reaction for A, Segment for B, and Number for C.

4. For the Input Variables, choose Left Ankle Reaction, LFO,and Bodymass for A, B, and C, respectively.

5. To the right of the function, select from the Reorder list to choose how you would like to output the joint forces. For comparison to Plug-In Gait, leave as XYZ.

6. To compare with Plug-In Gait outputs, from the Negate list, select  - /+/-.

   

7. Copy and mirror.

To extract joint moments:

1. Create a new variable called NormalizedLeftAnkleMoments.
2. For the function type, specify Kinetics and for the function, select Extract moments from reaction A in segment B's reference, C normalize.

3. For the Input Variable type, select Reaction for A, Segment for B and Number for C.

4. For the Input Variables, choose Left Ankle Reaction, LFO,and Bodymass for A, B, and C, respectively.

5. To the right of the function, select from the Reorder list to choose YZX. This ensures that the flexion-extension axis (in this case, ankle dorsiflexion) is the first component.

6. To compare with Plug-In Gait outputs, from the Negate list, select  + /-/+. 

   

7. Copy and mirror