GH Reaction - Comparison with Bergmann


I’d like to validate my values by comparing them with Bergmann’s et al. I use the standing model (Anybody V4) and commented the GHReactions.any out. As far as I understood I have to look at the GHMomentMuscles, coz it doesn’t include the Joint Reactions, just the moments and force generated by the muscles.
But the moments I get are higher than Bergmann’s. He has a absolute value of 0,29 and mine is about 0,7 or so. And the forces are totally different as well :confused:

When I look at GHNetMoments and check the values from there, the forces are almost 0, but I obtain the same moments as form GHNetMomentsMuscles. Shoulnd’t they be actually 0?

Anyways, I am just wondering why my values ain’t equal with Bergmann’s. Are they just a bit higher because of the simulation with software?

Best regards

Hi Hauke,

If I understand correctly you have commented out the GHReactions.any file from the joints definition. I think you should not do that, this file is important as it creates the joint reaction force. The model should not even be able to run without it unless you add an AnyReacForce here.

Then if you want to see the moment generated by the muscles only it is correct that you have to look at the GHNetMomentsMuscles. You can actually find that measure in the SelectedOutput folder in the ChartFX.

However you should make sure that you are comparing the right thing. I don’t know in details Bergmann’s work but i have the idea that if he measured moments on the shoulder prosthesis they don’t really represent the muscles action of lifting the arm, but rather some internal reactions related with the friction between the sphere and cup of the prosthesis for example.
That would explain the difference between the moments.

Best regards, Sylvain.

To quote Bergmann et al. :

“A clinically established shoulder implant (Biomodular, Biomet Inc.,
USA) (Mackay et al., 2003) was modified to measure all six components of
forces and moments acting at the humeral head (Fig. 1). Six semiconductor
strain gauges (SG, type KSP 1-350-E4, Kyowa) served as sensors for
the neck deformations and were placed in the hollow short neck between
the head and shaft.”

Hi Hauke,

Well this actually confirms what a was suspecting. The moments correspond to the deformation of the implant’s neck. This cannot be compared with the moment generated by the muscles around the joint. It is different.
But it is ok to compare the reaction forces.

Best regards, Sylvain.