We have developed a hardware and software platform, the WiiEMG, for controlling the Wii™ video game console with surface electromyography (EMG). WiiEMG is intended to assist with training and performance assessment of myoelectric control of upper arm prostheses. For this application, a player wears skin surface electrodes over myoelectric control sites. A real-time signal analysis system acquires amplified EMG signals and classifies the activity patterns associated with different motions. In addition, the amplitude of this pattern is used as a velocity signal, which is differentiated to give acceleration. Finally, a scaled version of this acceleration value is input as an analog voltage into a modified Wiimote™ in place of the normal accelerometer, and the Wiimote communicates the data to the console. To evaluate the system's performance, six able-bodied subjects were used to test the WiiEMG by playing the game Wii Tennis™ using myoelectric control. Results are reported that show how users develop improved EMG control after only a few brief trials. Improved muscle and EMG control has the potential to benefit myoelectric limb use as well as motor skills rehabilitation.