The suit's "voluntary control system" works by capturing bio-electrical signals detected on the surface of the skin, before the muscles actually move. The system analyzes these signals to determine how much power the wearer intends to generate and calculates how much power assist must be generated by which power units. The power units then generate the necessary torque and the limbs move. All this takes place a split second before the muscles start moving, allowing the relevant robotic joints to move in unison with the wearer's muscles.
I'm not sure calling this thing "HAL" was the best marketing decision. I don't envy the person whose exoskeleton decides it has better things to do than, say, lift bricks.