Muscle force from computed muscle control

[Brandon Brown]

Hello all,

I am performing a study in which I obtain muscle forces during throwing. I've done this using both CMC and static optimization. It appears that CMC allows forces which go above the maximum isometric force and seem to be quite large compared to what I get using static optimization. Does anyone have any ideas why this would be?


Thanks

[jimmy d]

Hi Brandon,

two things; (1) the force-velocity relationship of a muscle dictates that the fibers can generate a force greater than the max isometric force if lengthening.

(2) static optimization does not include a parallel elastic element

It sounds from your description that the differences seen between CMC and SO may be due to the passive component of muscle being missing in SO. I would also check the velocity of the muscle as well and see if its lengthening.

Let me know if that makes sense,
-James

[Brandon Brown]

Hello James,

What you have said makes sense but I don't think it can be the issue in my case. I have uploaded a document showing the triceps long force from CMC, static optimization, fiber length, activation and an associated EMG file that I obtained while performing the experiment this data comes from. If you look at the period of time for which the force from CMC is large, the fiber lengths are constant and not lengthening so I don't think the force should be greater than the maximum isometric force during this time period. I also don't think it's possible that the difference could be due to a lack of a passive element. The forces seem way too large for this to be the case. Static optimization and the activation I get from CMC actually correlate well with the EMG data. I'm not sure what the reason for the discrepancy could be.

Again, any help would be appreciated.

Thanks, Brandon

[Brandon Brown]

Hello James,

One final thing, I've been using the Thelen muscle model but the generic model was using the Schutte_Debrecated before. Could this be the source of the problem?

Thanks, Brandon

[Brandon Brown]

Hello everyone,

The reason the computed muscle control forces were going beyond the maximum isometric force is because the passive forces were indeed very large at the elbow-flexion angle considered in my model. It is the active force and not the passive force that should be below the maximum isometric force. The total force is the sum of the active and passive forces. James helped me solve the issue.

Thanks,

Brandon