Neuro-muscular electrostimulation, as well as the voluntary contraction, involves a contraction phase (stimulation), followed by a rest phase (pause).
The REST phase is extremely important for the muscle; during the contraction, in fact, capillary circulation is necessarily blocked and, if the muscle would remain contracted for a long time, without an adequate resting phase, the so-called “ischemia” would occur, i.e. there would be a restriction in blood supply which could be very dangerous for human tissue.
Capillary blood flow, blocked during the contraction, but facilitated during the resting period, constitutes the main means of supply to the tissue; the muscle, in particular, takes all the elements necessary for the production of energy (oxygen, protein and various enzymes) from this.
The selection criteria of the STIMULATION and PAUSE times are, all things considered, quite simple, although necessarily empirical: the greater the intensity of stimulation, the shorter the stimulation phase should be in relation to the time of the resting phase. In substance: if a muscle is stimulated in order to obtain the maximum contraction, the contraction time should be limited to very few seconds and a resting period should be added between one contraction and the next which is equal to at least 5 times the contraction period.
In order to simulate the voluntary contraction, or simply render the stimulation less uncomfortable, it can be advantageous to add in a stimulation progression and regression phase; we will call the two new phases RISE and FALL respectively.