forces on the hand

[Jernej Camernik]

Hi,

I have an experiment where the subjects are holding to the handle (with only one hand) while they are being perturbed at the waist. I am using a full body model (FullBodyModel_SimpleArms_Hamner2010_Markers_v2_0), to do the inverse kinematics an inverse dynamics. For inverse dynamics I want to add an additional (beside the force plate data) external force - forces recorded at the handle. My question is, should I use the force vectors as recorded by the force sensor or should I reverse them? The reason for this would be since when the subject pushes handle forward, a positive force vector in X direction is recorded, when actually a force applied to the hand is in the negative X direction.

Thank you for your answer.

Best Regards,
Jernej

[jimmy d]

You would reverse the force. You need the reaction forces which act on the body.

[Jernej Camernik]

Thank you!

One more question. When I specify the external force from the handle which is applied to the right hand, what do I select at 'Force expressed in' and 'Point Expressed in'? Ground or right hand?

Thank you!

Regards,
Jernej