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.