Controlling the force-length curve...?


This concerns your Hill-implementation. After reading some (ref. manual/tutorial/papers) I can’t see a way to control the “width” of the force-length curve of the contractile element. I can control the maximum force and optimal/neutral fiber length for example, which is very important, but that might not be enough for my “force scaling efforts”.
Any ideas? Or even better, correct me, and tell me how to control the “width”.


Hi Jokke,

The width can be controlled by the optimal fiber length. A longer optimal fiber length will give you a wider force-length relation. The position of the optimum length relative to the joint angle can be influenced by changing the tendon slack length.

Greetings, Mark

Bonjour Mark! Ça va?
Adjusting the fiber length with also change the width because the width is specified as a percentage of the optimal fiber length, correct? But can I control this percentage? Or any other aspect of the shape of the curve (except the “height” using max force)?


Well, I guess in the muscle model we have only the following parameters available:

They all have an influence (some more than others) on the final force-length-velocity relationship.
What is it you would like to optimize?

I once made a small anyscript file which I used for teaching. It is called HillMuscle.any. Here you can demonstrate the influence of changes in the parameters on for example the strength.

Greetings, Mark

Thanks for the model. Trying it out I saw pretty much what I expected. For 1 muscle it is not that hard to predict the outcome, even though I “thought in the wrong direction more than once”.
Anyway, what I will try to do is, in short, to “force-scale” a body-model by utilizing measurements (that includes anthropometrics, external forces and joint moments). Catching up on literature (e.g. doi:10.1016/j.jbiomech.2005.06.005), I found which parameters that should be most important. All but one are easy accessible through AnyScript, and that’s the “width” of the force-length curve. Browsing literature, people have used different numbers for this “width”, even though around 50% seems to be the standard. The theory seems to stem from which lengths a single sacromere can produce contractile force. I sorry to say that I don’t know if this parameter should be considered a “material constant” or if it changes depending on the muscle or the individual subject. Perhaps, I can do without this parameter, but I think my movement data might suggest otherwise (clutch pedal operation). I definitely will use F0, Lfbar & Lt0 in my scaling efforts.
Any thoughts?


I also would suggest the following article:

It is a more practical view on how to fit your muscle model to measurements.

Cheers, Mark

I was about to refer to that one also in my last post =)
But thanks,

btw, if anyone else is following this thread, i can recommend these 2 "new" papers,
both are on the subject of "force-scaling" body models...