Muscle Activation

[Sabrina Amrein]

Hi,

I've got a question regarding muscle activation:
I performed inverse dynamics, getting reasonable values. So, I took the next step and ran static optimization. Again, the calculated forces look reasonable. However, when compared to EMG, the overall activation pattern does not match. Specifically, static optimization performs wheelchair propulsion without deltoid activation , while EMG shows distinct deltoid activation. I can imagine that wheelchair propulsion doesn't strictly require deltoid activation and Static Optimization finds a way to calculate the motion without activating deltoid. However, I would like to match muscle activation to what was measured with EMG. Is there a possibility to modify muscle acitvation in such a way that it can be used as input for Joint Reaction Analysis?

Many thanks!

[Nicos Haralabidis]

Hello Sabrina,

Are you also using reserve actuators at the shoulder joint? If so you should check their influence, as they might be very 'cheap' to the optimiser to use and are therefore been used as opposed to activating the deltoid muscle. If you are using them perhaps lower their optimal force and see what influence that has?

Hope that helps!

Nicos

[Jacob J. Banks]

If lowering the actuator's contribution doesn't do the trick, you can always develop an API which considers EMG. For a shameless plug, please see the attached abstract introducing our implementation of Cholewicki's EMG optimization method with opensim + Matlab (we are in the process of submitting a manuscript). Otherwise, the Griffith group's CEINMS toolbox is perhaps a more established and accessible approach (https://simtk.org/projects/ceinms).

[Sabrina Amrein]

Thank you both! My reserve actuators have already low optimal force values... I'll have a look at your suggestions, Jacob, thanks.

[Yixin Shen]

I have met similar problem. Have you solve it?