Inverse Dynamics and Muscle Analysis Moment Differences

[Caitlin McCleery]

Hello,

We have been running analyses using exercise motion capture data. When trying to verify the results, we expected that the Inverse Dynamics net joint torques would match the sum of the individual muscle moments from the moment files created by the Muscle Analysis part of the Analyze tool for each movement. Is there a reason these should not be expected to match, or could this mean there is something wrong with the model or the results?

Thank you!
Caitlin McCleery

[Colin Smith]

Hi Caitlin,

How are you computing the muscle forces (ie Static Optimization, CMC etc)?

If you are just running inverse dynamics and then analyzing the resulting .mot file, you have not actually calculated muscle forces required to generate the motion. I am not positive, but I think the muscle forces resulting from this analysis would be the passive muscle forces in the muscles based on the model poses you prescribed for the motion.

Colin

[Caitlin McCleery]

Hi Colin,

Thanks for your answer. I'm using Static Optimization to calculate the muscle forces, and using the force outputs from SO as the forces file input for the analysis.

Caitlin

[jimmy d]

This may be relevant:

viewtopicPhpbb.php?f=91&t=4504&p=13368&start=0&view=

[Caitlin McCleery]

Hi James,

Thanks for posting that. I'm using Muscle Analysis from the Analyze tool instead of the Force Reporter, does that make a difference or should SO force results not be used as inputs for the Analyze tool at all? Also, if they shouldn't, what should be input instead?

Thanks for your help!
Caitlin

[jimmy d]

How are computing the muscle force contributions to joint moments? Are you taking the muscle force and multiplying by the moment arm? It's not clear how you are computing the muscle contributions to the joint moment.

[Caitlin McCleery]

Yes, to compare the Muscle Analysis moment file and SO results I multiplied the forces found by SO with moment arms from the Muscle Analysis part of the Analyze tool. When I added all the individual moments and reserve torques (from the SO file), the solutions matched the ID net joint torque results but not the Analyze moments.

Thanks!
Caitlin