There are a number of variable factors to keep in mind in order to reach the best results with the minimum amount of effort. It is important to understand them well in order to develop a personal training programme which allows us to achieve our objectives. Not all types of equipment are the same, nor do they emit the same type of current, and not with all of them can you reach optimal results. In the same way, depending on the current used, the training may be uncomfortable with the experiencing of a prickly sensation, or it can be comfortable and perfectly bearable, as is the case with the electro-stimulators that use Compensated biphasic square currents. However, it is not just this that we have to keep in mind; there are a series of essential characteristics which are necessary to consider so that our training allows us recruit the voluntary muscle fibres which we desire and so that our physical response is optimal; that it adapts; and that we can make the most out of our electro-stimulation sessions.