Muscle force and activation

Hi ,
I have a question concerning the output from the invers dynamics – I am looking for the muscle forces (or activations). The muscle force is the “Fm” under the desired muscle, right? And the activation? It is “Activity”? But as I also found at the forum, this is probably not “activation” as I am used to. Muscle activation should be between 0 and 1. But here it is “The muscle activity is defined as f/N, here f is the muscle force
and N is the muscle strength, there is no activation dynamics involved, so the activity reflects the current force in the muscle normalized with the muscles current strength.” And my activation goes above one (2-10). That is why I later also get muscle forces that exceed the maximal isotropic force of the muscle. I expected that when the maximal muscle force is reached, the other muscles are forced to be more active, so that they help these overloaded muscles. But the only think that happens is the warning “Overloaded muscle configuration“.

Can anybody give me any comment on that? How should I explain that the activity and the muscle forces exceed their limits?

It sounds to me like I should scale the muscle strength (StrengthIndexLeg ?) so that I get the activation = 1 (so that I am sure that the muscles can do the job).


Hi Michala,

you should check out the muscle tutorial: especially chapter 5: “Activity is the muscle active state in fractions of maxmum voluntary contraction.”

I also recommend the literature of the inverse dynamics tutorial:

You are right, that an activity greater than 1 isn’t possible physiologically but in a computer program everything is possible what you want :wink: So you’ll have to check if you told the muscle function that you don’t want activations higher than 1 with the option:
UpperBoundOnOff = On;

I hope that helps.

Hi Patrick,
Thanks for the reply. The “UpperBoundOnOff” function was exactly what I was looking for.