Why Minimum activation cannot be less than 0.01 for Thelen2013 muscle?

[Jiang Ping]

Hi all,

I find that there is a constraint of minimum activation for Thelen2013 muscle.
OPENSIM_THROW_IF_FRMOBJ(get_minimum_activation() < 0.01,
InvalidPropertyValue, getProperty_minimum_activation().getName(),
"Minimum activation cannot be less than 0.01");

Why has it been added to Thelen2013 muscle? Why the value is 0.01?
Why other muscle types (e.g. Millard2012EquilibriumMuscle) do not have such constraint?

Thank you in advance,
Jiang

[jimmy d]

Details about the modeling choices for the Thelen2013 muscle can be found here. The choice of default values, like minimum activation, were choosen to reduce numerical singularities.