Static Optimization vs CMC

[Charles Khazoom]

Hi,

I have been wondering the difference between Static optimization (SO) and CMC, as the faster SO seems to yield similar results to CMC in many cases even if it is neglecting muscle activation dynamics. Why would someone want to consider muscle activation dynamics (thus use CMC) for walking, where the activation dynamics are probably so much faster than the slower, more impotant rigid-body dynamics. In particular, why was CMC prefered to SO in this paper :


Dembia CL, Silder A, Uchida TK, Hicks JL, Delp SL (2017) Simulating ideal assistive devices to reduce the metabolic cost of walking with heavy loads. PLoS ONE 12(7): e0180320. https://doi.org/10.1371/journal.pone.0180320


Thank you for your help !

[Christopher Dembia]

The separate 'excitation' and 'activation' variables obtained when using CMC are typically expected of models of energy expenditure, and activation dynamics is important to model the fact that muscles cannot generate force instantaneously.

Furthermore, CMC supports compliant tendons, OpenSim's SO does not. Compliant tendons are important for accurately modeling the behavior of long tendons, such as the Achilles.