Spatial recruitment: the percentage of muscular tissue being stimulated is indicated to us by the current applied. In standard sports training we can also speak of spatial recruitment; light training involving less spatial recruitment than intense training. Walking requires less muscle fibre recruitment than an intense run. The more speed or strength required in training, the more spacial recruitment will occur; which is true of track training as much as with the electro-stimulator.

When we use electro-stimulation on quadriceps, there is no doubt that there will be a greater recruitment of muscle fibres as we increase the intensity (the amplitude). As the energy density applied on the muscles rises we will stimulate more muscle fibre, and in doing so, will increase the training level. Therefore, it is essential to consider that we will need a type of current which allows us to support raised intensities, as it is with these that we will be able to recruit more and more muscle fibres, so as to work the muscle to the point of inducing the adaptation which we require.

The mission of the muscles is to contract and, in doing so, act on the joints, causing movement. At the end of the day, it is for this that they are designed, for movement, although a contraction can be experienced without movement of the joint. However, both with isotonic and isometric movements, the type of movement and contraction will be regulated by the action potentials which will arrive to the muscular fibres. This we can identify by the intensity of the current which we apply, and by the spatial recruitment; a greater current intensity causes a greater spatial recruitment.However, the action potentials can be caused according to a determined rhythm; a guideline which we will call ‘frequency’, and we will see that changing the frequency, we can also achieve a raise in the number of muscle fibres involved in the contraction. As we raise the frequency, to a determined point, the temporal recruitment rises. To improve the level of spatial recruitment, it is essential that the electrodes are correctly situated on the specific motor points for each muscle group. The skin on which it’s placed should be as clean as possible, free of hair, grease or dirt, and good electro-stimulation equipment should be used.

In the same way that in voluntary training, with time and with the passing of each preparatory session, our tolerance to the strain and adaptation to it will improve, we will be able to bear higher intensities with the electro-stimulator with more comfort, and in this way, the results will be more and more visible, and with greater ease.