Muscle-tendon length VS normalized fiber length

[Giulia Cernivani]

Dear Opensim support,
for my thesis project I have to compare the differences in the length of the muscles of children with CP and in the control group. I have scaled the model, loaded the motion and performed the Analyze tool. I want to study the muscle-tendon length but I don't know how to normalize the values between the subjects for comparing the results. I can't understand if I should use the normalized fiber length or not.
Thank you very much
Best regards
Giulia

[Mohammadreza Rezaie]

Hi, for between subject comparison, you need dimensionless quantities. For Length (e.g. stride length or muscle-tendon length), it is suggested to be normalized by the subject's body height or leg length.

In case of rigid tendons, fiber length = muscle-tendon length - tendon slack length. So, they have similar pattern during movement. NORMALIZED fiber length = fiber length / its OPTIMAL length

Hof, A.L. (2018). Scaling and Normalization. In: Handbook of Human Motion. Springer, Cham. https://doi.org/10.1007/978-3-319-14418-4_180

[Giulia Cernivani]

Thank you very much!!!
Best regards
Giulia