Active fibre force, passive fibre force and body masses?

[Darius Nahavandi]

Hi,

We are using a full body model (ULB Project) for our analysis.

We noticed that the upper body fibre forces (total) calculated from OpenSim contain NaN values. However neither the active fibre force nor the passive fibre force returned NaN’s. In our understanding “total fibre force=Active fibre force+passive fibre force”,

1. However it looks like OpenSim calculates the Active fibre force, passive fibre force and total fibre force separately. Is it so?
2. Trying to look more into the problem we noticed that there are no mass and inertia assignments to the upper body. Our guess is this is effecting the total fibre force calculation. If so then why is it not affecting the active or passive fibre force calculations?
3. Is there a suitable reference we can find to calculate the upper body masses and inertias?

Regards
Darius

[jimmy d]

What analysis are you using? The active and passive components can be calculated just from the known length. The total force can just be an addition of these but I am not sure where you are getting each of these from. If the model doesn't have inertias and masses then the results of a simulation will be incorrect.

For masses and inertias I would look up the work of Katherine Saul and Wendy Murray.