Electromyography (EMG) is useful in investigating muscle activation; however, noninvasive evaluation of the raw surface EMG with voluntary muscle contraction has been limited due to its complicated waveform.The EMG waveform is superimposed of motor unit action potentials (MUAPs) with several muscle fiber types of various amplitudes.The waveform depends on the motor unit sizes and amplitude attenuation, in association with the distances or directions between the motor units generating the action potentials and the attached surface electrodes.