# Objective function & coactivation

Dear AnyBody Team,

I have some questions:

1. I am using the MoCap Model (AMMR 1.6.2., vers 6.0) and I would like to know something about the objective function. From the tutorial I see that the objective function for me thrid order polynomial would be the sum of (Fi/Ni)^3
Is this correct? And what exactly is N? In the tutriol I only found “Ns are some choice of normalization factors. Thinking about the physiology we might quickly get the idea that it is reasonable if strong muscles do more work than weak muscles, so the Ns could be measures of the strength of each muscle.”

2. Concerning coactivation of muscles: I know that when using a polynomial recruitment synergies between the muscles are allowed to a certain extent (increasing with higher polynomial orders). But how is it actually concering muscle coactivation? Is AnyBody able to take muscle coactivation into acount? And if so, how?

It would be great if I could get some help from you conerning my two questions.
Thanks,
Nathalie

Hi Nathalie,

Hope it helps,

AnyBody Team

Hi,

sorry I have to catch up on this again:

I have used the third order muscle recruitment (Fi/Ni)^3.
However, I am still not quite sure what parameter AnyBody uses in this standard setting for Ni?
cross-sectional area? isometric force?

where in my AnyBody project can I find this information?

Nathalie

Hi Nathalie,

Please have a look at this tutorial

This should explain it

Best regards
Søren

Hi Nathalie,

The default Ni is now described here. Briefly, Ni in AnyBody is muscle instantaneous strength, which can be F0 if a simple muscle is used and can be fce(l)*fce(v)*F0 (where fce(l) and fce(v) are the normalized force-length and force-velocity relationships of the contractile element component) when a two or three-element Hill-type muscle model is picked.

Hope this helps,