A pneumatic cylinder is being controlled by varying the rate of air pulses sent to it - mimicking the activation signal sent to muscles by motor neurons.  Air valves control the two directions of movement similar to the flexor and extensor muscles of a limb.  In addition, the compliance of the joint can be varied similar to that of an antagonistic muscle pair.

    The actuator design was conceived by John M. Hart (Electrical Engineer) and evaluated and improved by Jan Cocatre-Zilgien (Biology Researcher) during tests normally performed on actual muscle.