Isometric quadriceps controaction on an isokinetic device

I’ve simulated a human who is using isokinetic device. He is performing isometric contraction of quadriceps muscle in different knee angles. I’d like to find out the angle in which the subject produces his/her maximum torque.

I’ve performed the following modifications on a copy of “FreePostureMove” model: (1) This model uses two types of fixation (rotational and linear) on the pelvis. I have displaced these fixations (rotational and linear) to thigh and pelvis nodes. (2) I’ve also placed force and moment respectively on the back of ankle and knee.

The first problem is that when I run CalibrationSequence Operation, before InverseDynamics operation, the software always encounters overload muscle configuration.

In the angles of 10, 20, 30, …, 140 degree, I increased the force excerted to ankle untill I obtained the “overload muscle conficuration” error. I named this force as the “maximum durability force” and recorded this force for every angle.

The second problem is that the angle in which quadriceps muscle produces the maximum torque changes (it shouldn’t change) when I change (1) the plac in which my body is fixed, (2) When I replace torque with force.

Sahand University of Technology
AMS300-F License
AnyBody 4.0.0
AnyBody Managed Model Repository 1.0

Hi Saeed,

The first point - does this overloading sound as “over-stretched” during the calibration sequence, which may be ok, because it will calibrated in the next calibration study; or “over-loaded” when you run the inverse dynamics analysis? If the latter is the case: it just means that the muscle strength in the model is too low to perform this task.

What forces and moments do you use?

And the second point: could you send a screenshot how these two different fixation look like? And possibly the constraints code?

Are you sure that the force is equivalent to the torque (check moment arms)?


Muscle without strength : The muscle has been stretched too much

Whenever I use the zeijag muscle on FreePostureMove, with or without running Mian.HumanModel.CalibrationCalibrationSequence, I recieve tens of errors saying:

Muscle without strength : The muscle has been stretched too much

Question) What does it mean?

In AMMR1.0 > Application>Examples > FreePostureMove > Main.any just before #include BodyModelMus_3E it says:

The include file below selects the three-element Hill-type muscles. They require calibration before they can be used, and this can be done by the HumanModel.Calibration.CalibrationSequence operation.

But in AnyBody Tutorial > Inverse dynamics of Muscle Systems > Lesson 6 Calibration it uses AnyBodyCalibrationStudy

Question) What is the difference between "AnyOperation CalibrationSequence" and "AnyBodyCalibrationStudy"?
Question) Why does it keep giving me errors even after running "AnyOperation CalibrationSequence"?

I used AnyBody Managed Model Repository 1.0 and AnyBody Modeling System 4.0 for this.

Dear Saeed,

I did read your first and last post and I don’t fully understand, so I need to ask you again:

Do you get the “Muscle without strength : The muscle has been stretched too much” during the inverse dynamics simulation?

Additionally, AMMRv1.0 and AMSv4.0 are very old. It’s tough for us to give advice on that.

Do you get the "Muscle without strength : The muscle has been stretched too much" during the inverse dynamics simulation?

Yes. What does it mean?

I was wondering if you could please also consider the other questions in my second post. thank you.

Dear Saeed,

to your questions:

  1. In the 3E muscle model the strength of a muscle is computed based on muscle length and other parameters. Therefor the initial length of muscles has to be calculated which is done in an AnyBodyCalibrationStudy

  2. The difference between is that the one is a Study, the other is an operation (or more precise an operation sequence). To calibrate the muscles in the body model, AnyBodyCalibrationStudies have been defined for the different body parts. Each of these studies has an operation which performs this calibration. In the AnyOperation CalibrationSequence the operations of the Studies are listed as one sequence which starts each of these operations.

  3. I am sorry but I cannot reproduce that. I do not get a singe error when I run the FreePostureMoce.main.any. What I get are some warnings saying that the muscle has stretched too much (the text you wrote in your last post). Opening an AnyChart (or in AMS 4.0 a ChartFX) and displaying the corresponding muscle, we can see that the strength of the muscle goes down to 0. This can happen when the muscle gets too long and due to the muscle model cannot produce any force.

Best regards