simtk.org

Hi Allison,

My question is in regards to the Yr5 right turn data. I know you guys have done an excellent job making sure the data is correct and accurate, yet I sill have an issue that someone might help clarify.

When I view the GRF data for the right turn trial #6 (PS_rightturn6_grf.xls), I see only one clean force plate strike. What I see is that the GRF for the trailing (right) limb seems incomplete (I see a discontinuity and reduced magnitude), and I don't see data for the right leg after the left leg is on the first force plate. Considering this, I'm not sure how to generate a complete gait cycle.

Any ideas?

Thank you,

Zach

Hi Zach,

You are correct in that there is only one clean force plate strike for the right turn trial #6. As the subject turned during the trial, he did not hit cleanly the force plates with his right leg. So, there is no GRF data for the right foot at the end of the gait cycle. There are several ways to approach this problem and it will depend on what methods you are using. So, could you provide me with some more information about how you are generating your contact force predictions? Are you using an inverse or forward dynamics simulation? Do you have a foot-ground contact model or are you applying the experimental GRFs to the foot?

Allison

Hi Allison,

We generate our knee joint contact force predictions by applying experimental GRFs to the foot during an inverse dynamic simulation. I now realize that the absence of this data may have been by design to encourage participants to explore alternative approaches...?! I will explore using a ground contact model, unless you have any additional suggestions?

Thanks,

Zach

Hi Zach,

Given that you are doing inverse dynamics, you should be able to calculate your knee contact forces during the time when you do not have experimental GRF data. The only issue will be that you will have large pelvis residuals when you do not have experimental GRF data (because the motion and external forces will not be dynamically consistent). However, the large pelvis residuals should not impact your knee contact force predictions.

We always encourage competitors to explore unique approaches to estimate contact forces!

Allison