We review the many causes of motion artifacts in biopotential recording. We moved several electrode materials at several velocities in electrolytes. Artifact voltage ranged from 350 μV at 0.13% NaC1 concentration and 100 mm/s to 10 mV at 1.3% concentration and 25 mm/s. We present a theoretical model in which adsorbed ions attach to the electrode. Ions in the diffusion layer move with the electrolyte. This separation of charge causes the artifact. A second source of motion artifact is cable movement. This causes the polarization potential of the electrodes to have a varying attenuation because the stray capacity of the electrode varies. Experimental and theoretical artifacts ranged from 1 to 100 mV. Artifact is reduced by using electrodes having large area, electrolytes having high concentration, amplifiers having high impedance, and preamplifiers located at the electrodes.