We see that we can set out to raise the load work, whether it be to improve the quality of the muscle strength or speed, by raising the intensity of the current. There is a second way of increasing the load level and therefore improving the muscle strength and speed with the current electro-stimulators. This second type of work is temporal recruitment which implies that we will send a continued series of electric stimulus, without allowing the muscles time to relax. With an electro-stimulator we can achieve muscular tetanisation by raising the frequency. The muscle is subjected to impulses which create tension; this is repeated before the muscle has time to relax. The new impulse comes with the same intensity as the other contraction, which accumulate and produce a high degree of muscular tension.
It is difficult, if not impossible, to obtain tetanisation with low freqencies, as low frequencies act mainly on slow muscle fibres. Even with frequencies of 4, 6, and 8 Hz, the number of impules is not enough for efficient strength or speed work. However, these low frequencies are associated with muscular action resembling a massage effect, because of the relaxing and pleasurable contraction. This, as we will see, is useful when applied to muscular relaxation, as well as to improvement in the local vascularisation.