include-negative_mechanical_work in Metabolic cost estimation

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Ratna Sambhav
Posts: 42
Joined: Sat Jan 12, 2019 10:16 am

include-negative_mechanical_work in Metabolic cost estimation

Post by Ratna Sambhav » Sun May 03, 2020 5:18 am

Hello,
I am working on calculating metabolic cost when arm26 model lifts a load of 0kg, 1kg and 2kg from 0 degree elbow flexion to 95 degrees elbow flexion. So, this is the plot I obtained of total metabolic cost.
Picture1.jpg
Picture1.jpg (54.69 KiB) Viewed 277 times
But here I see that the metabolic rate curve for 2kg load is coming at some points even lower than that of 1kg and 0kg load. I don't understand this because with increasing the load, muscle forces are increasing and so are the muscle activations, and since metabolic cost is direct function of these quantities, it should also increase at every point. So, curves for 0kg, 1kg and 2kg loads either have to be parallel to each other with enough separation between them or if not linear then at least enough separation has to be there with no crossings.

Now, when I remove include_negative_mechanical_work_rate, the results are coming exactly as expected.
Metabolic_Rate.JPG
Metabolic_Rate.JPG (90.59 KiB) Viewed 277 times
I have read the Bhargava and Umberger models for metabolic cost estimation, but I am not getting able to understand what this negative_mechanical_work_rate is.

If someone has some idea regarding this the please help.

Thanks,
Ratna Sambhav

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Thomas Uchida
Posts: 1798
Joined: Wed May 16, 2012 11:40 am

Re: include-negative_mechanical_work in Metabolic cost estimation

Post by Thomas Uchida » Mon May 04, 2020 6:37 am

This parameter is described in the API documentation for Umberger2010MuscleMetabolicsProbe, under the "MECHANICAL WORK RATE (W)" heading (https://simtk.org/api_docs/opensim/api_ ... ml#details). Additional discussion can be found in the papers listed there.

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