# Lever Arm Muscles

Hi, I have a question concerning the lever arms of the muscles in anybody. I would like to find out the different lever arms of the 2D Bike model.
If a muslce spans only over one joint the lever can be calculated by muscle velocity (LMdot) divided by the joint velocity.
Whats about if a muscle spans over two joints, how can I calculate these lever arm (to joint one and to joint two)? Thanks
Best regards, manuel

Hi Manuel

I am not sure there is an easy way… if the muscle spans two joints i suggest you simply move one joint at the time… the momentarm will then be dependent on the position of the fixed joint but that is the reality.

You could set up a parameter study which would set the one dof to a fixed value and then run the full joint motion for the other one. Then you should be able to create a surface for the moment arm as a function of the positions of joint1 and joint2. Subsequently the same should be done for the joint2 using fixed positions of joint1

Best regards
Søren

Hi Soeren,

Do you agree that the glenohumeral joint in AnyBody spans two joints, because of the artificial rake joint ?

If it’s the case, do I have to perform your parameter study, if I want to compute the lever arm of the deltoid ?

If it’s not the case, can you tell me if my way of computing the lever arm is correct ?

LeverArm = …Mus.deltoideus_scapular_part_4.LmtDot/(…Interface.Right.GlenohumeralAbduction.Vel[0]+1e-6);

Thank you.

Pierre

Hi Pierre,

It is true about the rake, in fact the deltoid spans these two joints.

Since the motion of the rake is linked up to the motion of the GH joint with a fixed rhythm you will not need to calculate the moment arm as if it had two individual joints.

The equation you have written look ok if you use the same measure to move the arm with.

Best regards
Søren

Hi Soeren,

Sounds good. I would like to explain the steps followed by the software to find the muscle forces. I read that we cannot consider that the software computes the joints moment first, because of the biarticular muscles.

So my question is: What are the exact steps followed by the software ? I cannot find any clear information about these steps in the tutorial available from the website.

Thank you

Pierre

Hi Pierre,

Rasmussen, J., Damsgaard, M. & Voigt, M. (2001): Muscle recruitment by the min/max criterion - a comparative numerical study. Journal of Biomechanics, vol. 34, no. 3, pp. 409-415.

Michael Damsgaard, John Rasmussen, Søren Tørholm Christensen, Egidijus Surma, and Mark de Zee (2006): Analysis of musculoskeletal systems in the AnyBody Modeling System. Simulation Modelling Practice and Theory. Volume 14, Issue 8 , November 2006, Pages 1100-1111. Elsevier, ISSN: 1569-190X.

There are also webcast available on recruitment
http://www.anybodytech.com/196.html
Features of muscle recruitment algorithms (John Rasmussen, 25. June, 2009)

Best regards
Søren

Hi Soeren,

Ok thank you. I already have these articles. I will read them again.

Pierre