The principle of electrostimulation (EMS) is to stimulate the peripheral nervous fibres with small electrical impulses transmitted by surface electrodes.

Using the electric impulses generated by Compex stimulators, we can stimulate different types of nervous fibres:

1) Motor nerves – those that impose a mechanical muscular response. Thus we can facilitate a muscular contraction.
2) Sensory nervous fibres – those which control pain effects. Therefore EMS can be utilised as an analgesic device to nullify pain.

The high quality electronic components of the Compex device allow the generation of optimal impulses. They have to fulfil two requirements:

1) They have to be very strong and thus allow the optimal recruitment of muscle fibres.
2) Whilst strong they must comply with safety and comfort, thus that the power is perfectly controlled so as to avoid electrical pains or burns.

Delivered by a current generator, the optimal impulses are perfectly rectangular, biphasic and symmetric, with duration depending on the muscle fibre type (fast, slow, intermediate) being stimulated.

The operating principle of electrostimulation is very simple and faithfully reproduces the processes involved in muscle contraction under the control of our brain. When we decide to contract a muscle, the brain sends the command in the form of electrical currents that travel at high speed along the nerve fibres. At the end of the run, these electrical currents excite the motor nerve that then passes the information to the immediate surroundings of the muscle and triggers muscle contraction.

With electrostimulation, the excitation is directly produced at the motor nerve by means of ‘optimal’ electrical impulses that guarantee efficacy, safety and comfort in use. Thanks to this process, the muscle cannot distinguish between a voluntary contraction (caused by the brain) and an electrically induced contraction: the work produced is the same irrespective of the nature of the command.

A muscle is composed of elongated, cylindrical cells: the muscle fibres. Several types of fibres can be distinguished depending on their speed of contraction: slow, intermediate and fast. The disposition and the proportion of the various types of muscle fibres are genetically determined. The fast fibres will clearly be predominant in a sprinter, whereas a marathon runner will have more slow fibres.

Consequently, the type of physiological properties required will vary from one sport discipline to another. The Compex programmes have been developed specially taking into consideration these physiological differences and the specific requirements for different muscular qualities, i.e. strength, explosive strength, endurance and resistance.

Compex devices generate electrical impulses. Each of these impulses is intended to trigger action potentials (AP) on the motor nerve fibres (or motoneurones). In response to an AP, the muscle fibres belonging to the motor unit of the excited motoneurones produce a mechanical elementary response, which is called a twitch. A twitch is a unit of work for a motor fibre in response to an AP. The twitch and the work it represents are entirely similar, whether the AP is triggered by an impulse or is generated spontaneously by the nervous system. This means that muscle fibres always respond to an AP in the same way.

The type of working power generated by muscle fibres varies according to the frequency of the impulses (repetition of the impulses). For example, a low frequency of 10 Hz (10 impulses per second) imposes a low working power on the excited motor nerve fibres. On the other hand, a high frequency of 100 Hz imposes a high working power on the excited motor neurones. Therefore, the kind of work imposed on the excited motoneurons depends on the parameters of the stimulation programme. In other words, work is controlled by the stimulation parameters.

We also know that the twitch duration responses depend on the type of muscle fibres. As mentioned before, we can distinguish slow, intermediate and fast twitch fibres, which obviously react differently. Moreover, differences in twitch duration are associated with variations of the frequencies that are necessary to reach the maximum tetanization of the fibres. Therefore, the frequencies used in electrotraining will obviously vary and will have to be adapted to the type of fibres that have to be tetanized.

Compex has developed several stimulation programmes taking into account this knowledge of twitch duration, the tetanization frequencies of the different types of fibres and the results of research and clinical studies. Each of these programmes is specifically based on the kind of muscle performance the user is interested in.