We know that an electrical generator, to produce a current flow, must be “closed” on a load. The load, in the electro stimulation, is represented by the muscle to be stimulated. The connection between the generator and the treatment area (load) will be performed by means of a pair of conductive electrodes, having the job to transfer the electrical potential (voltage) to the load (muscle). A closed circuit need at least a pair of electrodes; it should not possible to obtain a current flow with only one electrode. A current flow must always have an input point and an output point.
If the aim of the electro stimulation is to produce a muscle contraction, at least of the two electrodes must be placed on that muscle, but which is the best position? The better responding point, in a muscle, is the “motor point”; it is indeed by stimulating on the motor point that we can obtain a better muscular recruitment with less energy. The other electrode could theoretically be applied anywhere but in practice, it is advisable to place it proximally, on the same muscle.
If we have to stimulate two controlateral parts (two limbs), it is also possible to place the electrodes of the same circuit, over the two controlateral motor points (avoiding transtoracic stimulation).
In the below represented tables, you can see the most common motor points of the respective muscles, but don’t forget that motor points can change between subjects.
The motor point is the better responding to the electro stimulation, so that the better way to find it is to try different near points.