I have been using AMMR for my research on cervical vertebra loads and motions using C3D mocap data to drive the model for a number of movements. At this point it has been great.
However, in a slightly extreme neck extension (e.g. drinking from a bottle), I notice the joint reaction force within the cervical intervertebral joints (for almost all the levels), have a very perculiar curve. After looking into the individual cervical muscle contribution, I noticed one muscle that stands out - LumpedHyoid (see graph). I presumed this is simplification of all the muscles attached to hyoid bone.
The graph is showing individual muscle force (pink lines) as well as the joint reaction force in C5C6 IV level (black line). The x-axis is the % of task completion (0% neutral head position, 50% maximum neck extension, 100% return to neutral head position).
This LumpedHyoid (blue line) also seem to be contributing a significant amount of force towards JRF of the cervical spine (close to 100N!). Is there any suggestion how I could rectify this? (change the muscle strength, incopr the mandible model, etc)
You are free to change either the muscle or muscle model as you find fit.
The muscle model parameters can be changed here: Main.HumanModel.BodyModel.Trunk.MuscleParametersCervicalSpineRight.LumpedHyoidT1C0Par
If you right click one of the properties you can select "find in anyscript" and that will take you to the code file where you can alter the values.
Thank you for your reply anf the suggestion given.
I had a look at the script as well as the Lesson 7: Calibration of the muscle in the tutorial to understand F0 and PCSA.
The 'LumpedHyoid' was modelled as:-
AnyMuscleModel LumpedHyoidT1C0Par = {
AnyVar PCSA = 2.35*1.5; //Physiological Cross Sectional Area in cm2
F0 = .StrengthScaleSpine*PCSA *..StrengthRef.SpecificMuscleTensionSpine; //Maximum force output at optimum fiber length
};
AnyMuscleModel LongusColliT1C6Par = {
AnyVar PCSA = 0.3914; //Physiological Cross Sectional Area in cm2
F0 = .StrengthScaleSpine*PCSA *..StrengthRef.SpecificMuscleTensionSpine; //Maximum force output at optimum fiber length
};
I think I have found the literature that gave the PCSA for muscles surrounding the hyoid bone which is close to what being used here (2.35cm2). I am trying to understand why for this particular muscle model, the PCSA is being multiplied by 1.5 prior to being scaled, unlike the other muscles within this class folder e.g. LongusColli above.
I would be grateful if I could uderstand the reasoning behind this so I could change the strength confidently without missing out any important consideration.
I looked through the changelog of the code and cant seem to find exactly when the 1.5 factor was implemented - it is well over 5 years ago so before we had any good tracking system.
My best idea is to look at the references where the model was developed an see if they made a comments about it.
