Abnormal ankle joint reaction force

Hi there,

I recently finish some musculoskeletal modeling for running subjects, but the results showed that the ankle joint reaction force is too high (eg., over 20 times body weight). First question is that do you think this is problematic? Second, If I want to debug such issue, where do you suggest to start with? Thanks a lot.

Best,

Junfei

Hello,
I had somewhat similar problem after modelling, I had lot of reaction forces from my force plate which was twice the body weight, I use MOKKA to analyze my MOCAP models (c3d files), In MOKKA it gave me the same values, so i figured that the calibration of the force plates was wrong while mocap, thus giving me very high reaction forces from the force plates.

If we consider f=mg, for a static trail. the g parameter being the acceleration is almost zero, so the force needs to be equal to mass (in N). I would check this parameter first. just to make sure that my input file is correct and giving me reasonable values. you could also check your Human ground residual values in Anybody to make sure you have your values going to zero after stepping on force plates.

There is a way to scale your values in MOKKA Tools >Analog> Scale. this is only if your input data is wrong.

I hope this might help you somehow.

Hi Bharathhs,

Thanks for your reply. The GRF recorded in the running process is generally 2 times larger than the body weight (N) which was consistent with other studies. What I am here trying to know is whether the marker location at the ankle and knee would have a significant impact on the JRF results. If yes, how would we justify the marker location is correct. Thanks.

Best,

Junfei

Hi Junfei,

Please try to review the direction of the GRF wrt to the joints, the further away it passes from the joints the higher the moment arm and the higher reaction forces you will see.

Marker location can impact results by "misplacing" joint centers, thus getting a too high moment arm wrt. to a measured GRF. It can also be a misalignment between mocap and force-plates.. so try to ensure this was calibrated correctly.

Best regards
Søren

Hi Søren,

Thanks for your reply. As for the misalignment between mocap and force-plates, it was affected by the center coordinates of the force-plate, right? So as the direction of the GRF wrt to the joints. While I was doing the coordinates transformation of the force-plate, the center coordinates was adjusted accordingly. In this regard, I think the alignment between mocap and force-plates was correct. Would there be any method to test such alignment is correct or not? Thanks a lot.

Best,

Junfei

Hi Junfei,

It is not something which I have a lot of experience in, but an instrumented pole (with markers) can be used to exert forces on the plate which can then be compared with the measured direction.

Best regards
Søren

Hi Søren,

Thanks for your reply. Let me put this way, for the markers location, especially the one near the joints, should be aligned with the recorded markers based on eyesight. Is that correct? If our research focus are on the lower extremities, should we just focus the markers in the lower extremities or the whole body instead. We used to have some models optimization converged even the markers are far away from its recorded data. Thanks a lot for your help.

Best,

Junfei

Hi Junfei,

Some markers which are easy to associated with a bony landmark have a fixed position which is not optimized. These markers may need adjustment by eye if their location is not as in the experiment. For the other markers/directions which are free to be optimized no adjustments would be needed.

If you are working on the lower extremities the effect of adjusting markers on the upper body will be limited.

Best regards
Søren

Hi Søren,

Thank you so much for the information.

Best,

Junfei

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