PID Control in Abaqus

Hello all-
 
I was curious if anyone has experience/references for implementation of PID control systems into an Abaqus Explicit model. In my application, I'm controlling muscle activation signals to generate a desired motion of the lower limb.  I'm currently using an external program (Matlab) to implement the controller, update amplitude cards, call abaqus using the RESTART command to evaluate the next step in the model, calculate error, then repeat on the next step.  However, it seems like there should be a more efficient way using user-subroutines (like VDLOAD) to accomplish the same goal within Abaqus.  Suggestions on implementation and efficiency from anyone with such experience would be greatly appreciated.
 
Thanks in advance,
Chadd Clary
 
Post-Doctoral Research Associate
University of Denver