The model file has stretch reflex controller .xml tags, but you must download the .dll file from Matt Demers' Github (see above) and include the 
plugin by adding it in the OpenSim GUI. 

The disturbance force acts like another reserve actuator, except we specify its duration and magnitude. 

Use the attached MATLAB script to generate controls files with included disturbane forces. You can change the magnitude, duration, and direction of the disturbance force
easily, just change the corresponding variables under the "create the disturbance force(s)" header. 

The MATLAB script opens quietStance_initialStates.sto, which already has averaged values from CMC. In fact, one easy way to generate average values is to run CMC, choose a 
point in time at which all muscle activations cross the average value, and start a forward dynamics simulation from that timepoint. The initial activation values 
in the forward dynamics simulation will be the average values, and you can delete all other timepoints from the generated controls file.