I am planning to assess the joint movements and muscle response in the hand.
I am currently working with the freeposturemove model.
When i try to create a wrist flexion of 90 degrees, i can see that some of the muscles that are responsible for finger flexion are actively involved during this process. I can see these finger flexion muscle exhibiting some activity and change in power and length.
I know this is true in reality. When we flex our wrist, our finger also flexes involuntarily. But, i want to know if the same applies in the simulation as well because there are no drivers for fingers in the simulation to create that finger flexion.
Could you clarify if creating wrist flexion of 90 degrees in turn causes a finger flexion to happen automatically?
If so, is it possible to have a pure wrist flexion without having the finger flex?
Please let me know.
Short answer is no wrist flexion will not automatically flex the fingers.
The detailed hand model is not complete in the sense that the muscles spanning the wrist is not attached correctly to the individual finger bones, instead the muscles are attached to the carpal bones. The torques needed in the fingers are instead created by torque actuators, which is an simplification.
I am planning to use the model to analyse how the muscles/joints react to different motions. I am a PhD student.
I appreciate your answer.
I have one more question. While performing the elbow or wrist movements, some muscles responsible for finger flexion such flexor digitorum superficialis, flexor digitorum profundus and flexor pollicis longus also show some activity. If the finger don’t flex, when we flex our wrist, why are these muscles showing some activity.
Is it because these muscles are attached to the carpels, that when we move the wrist or elbow, these muscles also tend to expand/ contract during that motion ? If so, does this resembles what happens in a real scenario ?
To determine if a muscles will be active or not depends on the applied loads of the model, so external loads, dynamics, passive forces etc. When the muscle recruitment is being solved the solver looks for a solution which will minimize the activation in the muscles, while at the same time maintain dynamic balance in the model.
So it is often complex 3D balance mechanism that determine if a muscle will be active or not, it is too simplistic just to link it up to finger flexion or not.
Hope it helps.
Please see e.g.
2006 Damsgaard M, Rasmussen J, Christensen ST, Surma E, de Zee M (2006), " Analysis of musculoskeletal systems in the AnyBody Modeling System ", Simulation Modelling Practice and Theory, vol. 14, pp. 1100-1111.