"Manually" scaling GRF in gait2392 would provide reliable results?

[Daniel Pina]

Hello,

I will be trying to simulate how an added weight in the form of an orthosis in the scaled gait2392 model would affect the various muscles and metabolic cost.
I initially thought of adding the orthosis and contacts to the model, but I've seen many answers in this forum suggesting that performing CMC with contacts is rather complicated and could require custom code to run.

Considering the orthosis is "evenly displaced" around the whole lower body from feet to torso, how "unreliable" would it be if I just evenly increased the ground reaction forces already available for the model?

If the scaled model is ~73Kg and the orthosis is 10Kg, could I "simulate" the model as a 83Kg subject by running a matrix multiply of (83/73 = 1.137) to all the values in the grf file?



Thank you.

[Thomas Uchida]

how "unreliable" would it be if I just evenly increased the ground reaction forces already available for the model?

I would not expect that approach to produce reliable results because the GRF doesn't increase with load as you have described. For example, see Silder et al. (2013) "Men and women adopt similar walking mechanics and muscle activation patterns during load carraiage" (http://dx.doi.org/10.1016/j.jbiomech.2013.06.020), Figure 2.

[Daniel Pina]

Yes, I see now that the GRF doesn't increase linearly with the total weight, not to mention the inertia errors that would be associated.

Thank you!