I am currently researching into loads and motions in the cervical spine by using Plugin Gait MultiTrial StandingRef model that is driven by mocap data. One of the activities that I was studying is looking at neck extension which I captured using mocap of a subject drinking from a water bottle.
After running inverse dynamics simulation on AnyBody, we found a very peculiar pattern of axial loading on the cervical spine during neck extension. See graphs in photos. Solid black line is the axial laoding on C5C6 and other coloured lines are muscle activities. We felt the pattern of axial loading during this neck extension is not as what we expected. And we believe this is due to the muscle forces at interplay.
After reading through Muscle Recruitment topic here, I believe this due to the order of polynomial of muscle recruitment used given the sudden activation and deactivation of the muscle fibres particularly the extensor compartment.
If this is true, is there anyway I could tweak the model to be more physiologically accurate?
I notice that the 'Power' from the Criterion in Inverse Dynamics folder in 'Studies' is set to value '3'.
It sounds like some interesting work you are up to!
What axial loading and muscle pattern did you expect to see during the motion?
Did you enable the BM_TRUNK_CERVICAL_MUSCLES ?
If you are using the simple muscle models you can try using the 3-element hill types, they take force-length and force-velocity relationships into account, but they are hard to calibrate.
you can overwrite the Power to something else, but it is hard to talk about it being more physiological. Increasing it will allow for more co-contraction of the muscles while the opposite for a lower value.
No, the power is set per study and will affect all the muscles.
We were not expecting to have 2 sudden peaks (at about 25% and 75% of task completion) from the axial loading (see the solid black line in the graph).
BM_TRUNK_CERVICAL_MUSCLES was enabled. However, only simple muscle model option is available from _BM_CONFIG_PLUGIN (the other option is Off). Can I simply define _MUSLCE_3E_HILL_ for BM_TRUNK_CERVICAL_MUSCLES in "BodyModeConfig.any" or will this will break the simulation/model? I am using AMMR v2.3.0.
We are expecting to have more co-contraction between extensor and flexor compartment in this activity due to the imbalance of muscle bulk between the two compartment and maintaining the balance of the head whilst drinking from a bottle. And slightly less sudden of activation and deactivation between these groups.
Ok. But how do I overwrite/increase the power in the study as I can't seem to be able to change the value from the model tree above. Do let me know. Thank you.
We currently don't have ready to use 3-element muscle models for the cervical muscles - only those that are part of the arm model and you can enable them with the BM_ARM_MUSCLES_BOTH _MUSCLES_3E_HILL_ statement in the BodyModelConfig.any file. For the remaining cervical muscles you have the option of implementing 3e muscles yourself. If you start to use 3e muscles remember to run the calibration studies.
for 2 + 3 you can overwrite the power by adding Main.Studies.InverseDynamicStudy.InverseDynamics.Criterion.Power = 4; to your model. I would add it to the LabSpecificData.any if you need it to apply for all trials.
Thank you for your guidance. Just a quick clarification:-
When you say 'If you start to use 3e muscles remember to run the calibration studies.' you mean that I need to `RunParameterIdentification' again, aren't you?
No I actually mean the muscle calibration routines. AnyBody provides a one-parameter and a two-parameter calibration routine for the 3e-muscles that are implemented. The first calibrates the tendon lengths of each muscles thereby relying on the optimal fiber lengths that was given as input. The second routines calibrates both the optimal fiber lengths and the tendon lengths.
The study is self including when you switch on the 3e muscles and is located under: Main.HumanModel.Calibration if you don't run them the muscles will not work and you will see a lot of errors and failures.
