simtk.org

Hi,

I am looking to use AddBiomechanics to scale a model with walking and perturbation data. I previously ran into issues with scaling and RRA with the traditional OpenSim method, and ended up with very high residual forces. I thought using Addbiomechanics would be a better option, but I have two questions:

1. How does AddBiomechanics account for incorrect/inaccurate placement of the ASIS markers - specifically in larger subjects where it was impossible to place the marker on the ASIS directly. I believe this caused some of my scaling/RRA issues in the past.

2. How does the program tolerate custom models with limbs removed? I am using a model based on Rajagopal where the arms were removed and I redistributed the mass to the torso.

Thank you for any feedback,

Kaitlyn Downer

Hi Kaitlyn,

1. AddBiomechanics allows the placement of anatomical markers to vary slightly during the scaling process. Note that anatomical markers are penalized more than tracking markers when deviating away from the original marker placement.

2. Residual torques are applied to the model to ensure dynamic consistency during the dynamics fitting process. If you have limbs removed, these torques will be larger to make up for the missing information.

Best,
Nick