Why using force plate in gait analysis?

Hi,

Is gournd reaction force colleceted by force plate in c3d used in inverse dynamic study, or just for validation? I think gound reaction force can be calculated from body mass combining with MOCAP data, is it correct?

Thank you very much.

Hi,

I write this reply to discuss this problem with you.

As we know, the main external forces in gait analysis are ground reaction forces.
Additionally, we may need some pelvis residual forces and moments to fit the equations of motion.

The ground reaction forces in the single stance of gait may be predicted using proper human models and kinematic information because all ground reaction forces are applied at single foot. But in the double stance phase of gait, it is kinetically indeterminate problem.

By the way, you can try to solve this problem. In the ‘StandingLift’ example in AMMRV1.3, you can set the unknown ground reaction forces as ‘Conditional Contact Element’ model. It’s a kind of artificial muscle based on AnyGeneralMuscle class.
By the muscle optimization criteria that you selected, the ground reaction forces can be predicted.
But it is just one of the many possible solutions.
We can validate it by comparing the measured ground reaction forces and the predicted values.

I’m sorry if my reply may be boring to you.

Best regards,
Moonki

Thank you for your answer.

I am actually interested in lifting. Is that case, force plate may not be necessary, but I will use it to valid the lumbar joint moment predicted by AnyBody. I want to modify existing gain analysis model for my application, so I would like to understand it first. Your answer may help me a lot.

Thanks.

Hi,

I’m glad if my reply may help to you.

I’d like to tell you my additional opinion.

If you want to perform inverse dynamics to get the joint moments using predicted GRFs,
you should care the directions of two predicted shear ground reaction components.

If the predicted COP(center of pressure) and two shear ground reaction components may be different from the real measured values,
they would do different effect on ankle moments.
So I guess that the joint moments of lower body may be all different compared to the inverse dynamics result using real measured GRFs.

But the joint moments of upper body may not be problems by virtue of pelvis residual forces and moments.

I guess that your lifting simulation can be performed using AnyBody.

Best regards,
Moonki