# GRF Prediction problem

I am currently making model using GRF prediction code and Mocap model.
And I have a question about GRF code prediction.

The attached model’s motion file is walking in high heels.
I think that it does not make sense that the power of each node occurs discontinuously. Even if considering the error depending on the model in the shoe.
(So, I cannot predict CoP values depending on this.)

This is not a problem to be solved by simply changing the contact conditions. Because result of single support even has discontinuous values.
I want to know what kind of error is possible.

Thank you for always kind answers.

I question again that I think my question was not specific.

1. The activity and Fout of each node is not continuous.
2. There are nodes where there are no force even when it contact. I think distribution of force is unreasonable.

Taking all these together, I think that distribution of force in GRF prediction of this model is wrong. I want to know the cause of the error.

First let me try to explain, the CoP prediction is primarily depending on the motion and the masses of the subject.

The distribution at the foot can be altered using settings for the contact, such as heigth and strength.

If the height is set wrongly the subject will not be able to keep balance and large residuals are needed this will alter Cop predictions.

Now to the distribution of the forces on the foot, assuming the model is able to keep the balance without too large residuals the distribution can be altered changing the strength of the contact muscles.

So i would, First check residuals … then check the height settings then change the muscle stregth.

Best regards
Søren

The error output occurs not only at the beginning and end of the contact, but also in the single support phase.

In other words, in a phase where one foot touches the ground, there are nodes with and without force outputs. But every nodes are confirmed to be a contact. Is this also a matter of contact settings?

Or is the GRF prediction code specific to bare feet and is it difficult to apply to other shoes? (In the experiment, I tied high heels to feet and made them one segment.)

Thank you.

Hi

Please try to notice if the CoP comes close to the edge of the foot, if this is the case this explains why only a few are active, most likely it is a matter of the dynamics of the model.

Best regards
Søren