Difficulties adjusting Opensim to more ballistic and uncommon tasks

[Rodrigo Mateus]

Hello Opensim experts,

This is an open question to anyone who wants to intervene.

My focus of study are more ballistic tasks, such as cutting motions, A/P decelerations or stop jumps, performed at high velocities and with great power.

I have been an Opensim user for almost two years, and during this time I did my masters thesis which evaluated the muscle forces, joint reaction forces and individual contributions using generic MSK models (gait 2392) during an horizontal deceleration task in elite athletes.

Although the support pages from Opensim are helpful, they aren't helpful enough when these types of tasks are concerned, unfortuately. So, I have come across some roadblocks.

Firstly, regarding the RRA tool, how does it fare against these types of tasks?
- I could choose limiting the tracking errors in the tasks file available, but it turns out it will alter the net joint moments, which would change the muscle force estimations
- I could choose not to limit the tracking errors, and end up with translational errors of about 10 cm across the mediolateral direction, which are above the limits provided in the support page, but how concerning would that really be?
- In terms of number of passages and mass adjustments, is an initial mass adjustment of 9 kgs an indicator that there are errors in the data or is it just a matter of needing more RRA passages to achieve consistency?

Secondly, SO and CMC:
I have looked at the source code from github and tried several approaches to use these methods.
- How important is choosing to compute for auxiliary states in these analyses?
- Is there any evidence that points to the Milliard muscle model being more effective that the Thelen muscle model in these types of tasks? I searched, but did not find anything. Maybe some of you can help with that.


I know that the majority of works being done with this software is regarding running or gait, either pathological or normal, but if you could spare some of your time to help me draw some guidelines regarding these types of tasks would be really helpful please.

Thank you in advance,

Rodrigo