High values JRF

[LESSBY GOMEZ]

I have performed motion capture of the gait of a woman weighing 51 kg. I exported to opensim the data provided by OpenCap, ran the inverse dynamics and obtained with "analyze", reaction forces in the knee joint, higher than 20000N.
Does anyone have any idea what could be happening? Have you experienced similar problems?
Thanks

[Antoine Falisse]

Hi,

When you say "ran the inverse dynamics", do you mean you ran muscle-driven simulations as in this example? https://github.com/stanfordnmbl/opencap ... inetics.py

best,
Antoine

[LESSBY GOMEZ]

I ran it directly in opensim.

Captura de pantalla 2023-03-21 160743.png (30.55 KiB) Viewed 249 times

[Antoine Falisse]

To run ID in OpenSim, you need knowledge of external forces, such as ground reaction forces. If you used OpenCap to measure a walking motion, you only get the kinematics. If you measured ground reaction forces using force plates and synced the data with OpenCap data, then you could run ID. But if you only have the kinematics, then the output of the ID analysis will not be meaningful.

Another way to obtain kinetics is to run muscle-driven dynamic simulations. We have examples here: https://github.com/stanfordnmbl/opencap ... inetics.py

Please read our paper to learn more about such simulations: https://www.biorxiv.org/content/10.1101 ... 7.499061v1

Antoine

[LESSBY GOMEZ]

I. understand.Thank you very much

[Antoine Falisse]

No problem.