Abstract: An electrical muscle stimulator (1) simultaneously supplies a pulse (i.e., 270, 271) to each electrode (5, 6) having first and second phases (272, 273; 274, 275) which are a mirror image to the pulse supplied to the other electrode. A control is connected to unbalance either or both the width and amplitude of the first and second phases of each pulse to selectively provide an unbalanced stimulation to one or more muscles through the electrodes (5, 6). The stimulator provides a precise control which is readily adjustable for a large number of operating sequences.