This paper presents a control approach for a myoelectric transhumeral prostheses that supplements a typical two-site electromyograms (EMG) input with the inertial measurement of arm motion. The inertial measurement is employed to: 1) provide synergistic movement between the prosthetic elbow joint and intact upper arm and 2) to switch control between the myoelectric elbow and hand. In order to assess the prospective efficacy of the control method, experiments were conducted on six healthy subjects who performed a series of pick-and-place tasks within a virtual environment. The assessments compared the time required to complete the pick-and-place tasks using the proposed coordinated control approach, with the time required using a sequential control approach (i.e., the conventional approach used in commercial devices). Subjects on average completed the pick-and-place tasks 34% faster with the coordinated control approach, relative to the conventional sequential EMG method, with no difference in compensatory torso motion.