A small question about the difference of the scaling method

[Yingfan99327]

Hi,

I am a rookie in human modeling research. First, really appreciate that you created and open-sourced such a great tool for muscle parameters scaling for the OpenSim model!

I just have a small question and I am not sure whether I understand it correctly. So, the scaling method proposed in this tool for muscle optimal fiber length and tendon slack length scaling is totally different from that implemented in OpenSim?

Because as introduced in OpenSim scaling tutorial that a muscle’s new optimal_fiber_length and tendon_slack_length are computed during the scaling proces with a scaling factor, I guess the scaling factor is calculated internally based on the collected pose data.

So, am I correct that

1. The scaling methods for muscle length scaling in your method and the method used in OpenSim are totally different and your method could be used as a plug-in in OpenSim.
2. From the OpenSim scaling tutorial, I could do the scaling with static pose data. For your method, could I also only use the static pose data or I need to collect some motion data for muscle length scaling?

Sorry to bother you that maybe my questions sound a bit weird. Really appreciate if you could share any insights regarding these questions.

Wishing you all the best.

[Yingfan99327]

And as the introduction in the SimTK web that "This project presents an optimization based technique to adjust muscle parameters of models linearly scaled from a generic one and to obtain reasonable estimation of optimal fiber lengths and tendon slack lengths in models generated from medical images." So, does it mean that if I want to use this method for muscle length scaling, I need to collect the medical images data, only motion data or the static pose data is definitely not enough if I use your algorithm?

[modenaxe]

Hi Yingfan,
sorry for the delayed reply - better late than never!
Coming to your questions:

The scaling methods for muscle length scaling in your method and the method used in OpenSim are totally different and your method could be used as a plug-in in OpenSim.
No they are not. The OpenSim method is very similar, but only uses one pose of the models while this tool explores combinations of joint positions. The OpenSim scaling tool maintains the ratio of optimal fiber length and tendon slack length in the scaled model.

From the OpenSim scaling tutorial, I could do the scaling with static pose data. For your method, could I also only use the static pose data or I need to collect some motion data for muscle length scaling?
This method does not requires input data. It requires, however, that a scaled (target) and generic (reference) model have their joint reference systems defined in a consistent way, so that joint configurations in the two models are effectively corresponding (no offsets).

Does it mean that if I want to use this method for muscle length scaling, I need to collect the medical images data, only motion data or the static pose data is definitely not enough if I use your algorithm?
No, what I meant was that the method maps the normalised operative lengths of the muscles of the reference to the target model, independently from the target model you use: it can be scaled (so the same model as the reference model but with different segment lengths) or a model built from scratch, like in the case of models created from medical images. The paper hopefully illustrates this in details and also links to an OpenSim plugin that you can use.

I hope this helps!

Luca

[Yingfan99327]

Hi Luca,

I hope you are enjoing a nice day today!

So sorry for my late reply. Really appreciate your replies and answers to all my questions, they are sooooo helpful and insightful.

Thanks again and wishing you all the best.

Yingfan