Ground reaction force multiple plates

[Matteo Arquilla]

Hello everybody,
I'm using four force plates (two consecutive ones for the right leg and two consecutive ones for the left leg). I record the data of the four force plates so that they are only grouped for the left and right legs while I don't calculate the resultant ground reaction force vector for each side. In this way, if a single foot strikes simultaneously two plates, two differente force vectors of the same (right/left) group are recorded. I have two questions:

[*] I assume that even though I import in OpenSim two force vectors for each foot (and not the resultant ground reaction force) the inverse dynamics can still be calculated properly but I'm wondering if this assumption is right or if I need to calculate the resultant vector in advance.
[*] In the inverse dynamics tool, when setting the external loads, I apply the forces to the ground; is it correct or do I need to apply the forces to other body segments (e.g. the calcaneus)?

Thank you very much for your help.
Regards,
Matteo

[Dimitar Stanev]

Hi,

Each force is described by three columns (one for each coordinate X, Y, Z). You need to specify how you apply this force on the body segments and how this force is defined in the file (e.g. global frame or some other frame). If you go to the external force window (External Loads in Forward Dynamics Tool for example) you can specify all these settings. You can look into the examples in the model folder to see how they defined the force plates. The procedure is as follows specify a body to apply the forces, specify the frame you have measured these forces and the name of the force plate. You can apply multiple forces this way.

In the inverse dynamics tool, when setting the external loads, I apply the forces to the ground; is it correct or do I need to apply the forces to other body segments (e.g. the calcaneus)?

You apply the forces on a body segment and you measure your typically express your forces in the ground frame.

Regards

[jimmy d]

You can see an example of the this in your OpenSim installation (Models/Gait2392). The external loads files has two separate forces.