Once we have this graphical model, we need to be able to give it accurate predictions. This is the job of Optimal Control.
Optimal control is like a multi dimensional curve fitting technique.
You will remember that the torque values predicted by the model for certain EMG profiles do not initially match up with measured torque values because of various differences in our test subjects. Optimal control is responsible for adjusting the variable parameters in the model in order to make the predicted values as close to the actual values as possible.