Foot penetrates force plate

Hi Colleagues,

One of my subjects's foot penetrates the force plate. This is quite abnormal given that every other subjects looks fine.

For scaling, I used LENGTHMASSFAT.

Here is a screenshot of the plantar aspect of the foot on force plate as reference
foot penetrate force plate

Has anyone encountered such before? what could it be?

Regards,
Kachi

Hi Kachi,

This must relate to the markers, it is hard to see but it looks like there are some large marker errors.
Did the model finish parameter optimization and are foot markers placed correctly?

Best regards
Søren

Hi Søren,

Thanks for your response.

The model completed parameter optimization. I suspect the xiphoid marker. It is strangely positioned lower than expected.

I'd share a picture of it when I resume at work tomorrow.

Thanks,
Kachi

Below is a image of the model after inverse dynamics.


The foot still penetrates the force plate.

I observed that the xiphod marker is strangely placed far below where it was during the laboratory trial. Also the centre of pressure and markers of the left foot appears to be outside the foot.

I look forward to your response.

Regards,

Hi Kachi,

It looks to me like the foot markers has been allowed to be optimized too much, and then they have found a location "outside" the foot.

I think you need to look at the markerprotocol and turn off the optimization of some of the foot markers.
It seems to happens only on Left side so compare the left/right optimization settings (OptX,OptY OptZ) for these markers that you have these symmetric. Notice the Green/Red arrows in the model when you are doing marker tracking.

Best regards
Søren

Hi Søren,

I have turned off the optimization of the foot markers. I also included a weak driver for the hip and ankle. The foot still penetrates but the markers look better

What other options do I have?

Regards
Kachi

Hi Kachi,

I would move the foot markers a bit up on the foot... so change the sRelOpt value in the markerprotocol.

Visually it looks wrong, but i do not expect this to impact results a lot.. the force is still applied as it was measured.

Best regards
Søren

Hi Søren,

Thank you for your response. I have tried to make the adjustments based on your suggestion. It still penetrates the force plate.

I tried to also look up past posts on this forum to see if someone else have similar challenge but couldn't find any.

Is there anyone having similar problems and what other steps was taken to fix it. Though the results wasn't affected, I don't feel fulfilled knowing that there is a problem somewhere in my work.

I look forward to hearing from you and other who might have suggestions.

Regards,

Hi Kachiozo,

I read my previous answer again and realized i should have suggested to move the marker downwards and not up. Moving it down should have the desired effect, sorry for this.

Best regards
Søren

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