This paper describes an extended manipulability measure for robot arm based on bi-articular muscle principle. There are several manipulability measures for serial link manipulator. However they can not be applied for manipulators which has animal-like actuator alignment. Bi-articular muscle is an unique actuator of animals. It connects two joints and drives both simultaneously. Conventional measures does not consider such actuators. We extended Impedance Matching Ellipsoid (IME), which is an unified measure. Proposed measure considers animal-like actuator alignment including bi-articular muscles. For verification, we measured actual output force of robot arms. Whereas proposed measures can represent actual characteristics of the robot arm equipped with bi-articular driving mechanism.