Subject-specific muscle parameters

[Pei-Hsin Kuo]

Hi,
As I understand so far, OpenSim linearly scales the optimal fiber length by using a scalar factor. Does any paper published provide the detailed information of how the scalar factors work through the anthropometric scaling? And, how do I scale the maximum isometric force for each muscle in OpenSim?

Thanks for the huge help
Pei-Hsin

[Bo Ding]

Hello Pei-Hsin,
I have the same question with you, and I wonder know have you figured out a solution to this problem. I would appreciate it if you could tell me how to match the model to the specific subjects.
Thanks very much. I look forward your reply.
Bo Ding

[Glen Lichtwark]

This is an interesting question. Generally, there is not a strong relationship between an anthropometric variable like height or leg length and muscle fibre lengths in more distal muscles that have long tendons and short fibres (e.g. gastroc, soleus, tib ant). There is very large variation which is likely linked to other factors like muscle size and tendon compliance etc. However, the following paper is probably the best that shows a moderate relationship between age (and tibia length) to gastrocnemius fascicle length -

http://www.ncbi.nlm.nih.gov/pubmed/21635250

Hence, I think that the linear scaling of length is probably justified, however subject specific measurement would be much more accurate. Given the simplicity of the muscle models used, then the scaling of fibre lengths probably makes very little difference to most simulation solutions.