Higher Joint Reaction force at Cervical spine

[Abdullah Al Masud]

I am working with the combination of MASI model and Hyoid model for a neck flexion and extension simulation. I have used ground reaction forces to calculate the joint reaction forces at cervical spine (C1-C7). In addition, I performed Static Optimization to calculate the muscle activity although it showed the Optimization was failed. I am assuming that it is due to not having enough actuators. When I calculated the joint reaction forces at C1-C2 level, I found the reaction forces are too high (attached figure). Then, I increased the actuator values (5 times) of the neck muscles and I found a reasonable joint reaction forces.

Do you have any suggestion to resolve this issue? Do I need to add any other muscles/actuators? If I need to increase the actuator's value, what is rationale behind it? Thanks for your time.

[Abdullah Al Masud]

I really appreciate your suggestion.