Resumen en español

The functional electrical stimulation is a technique of rehabilitation for patients with paralysis that restitutes the lost motor function, which can be studied by means of the registry of the electrical activity of muscles or electromyographic signal. When the muscle is being stimulated, this signal is a wave of synchronous depolarization with the stimulus, which receives the name of M-wave. This wave is the main indicator of the answer of the muscle to the electrical stimulus and presents changes in its spectral and morphological characteristics when the fatigue phenomenon appears. The muscular fatigue limits the use of systems of functional stimulation during prolonged periods. The variables more used to evaluate the changes in M-wave are their amplitude and duration, and the mean and the median of their frequency spectrum. During the fatigue phenomenon, the amplitude of the M-wave diminishes and its duration increases. As a result of the lactic acid accumulation, the speed of conduction of muscular fibers is reduced, resulting in a spectral compression and a shift of the frequency spectrum towards the low frequencies. The reported works that study the changes in M-wave during the occurrence of the phenomenon of fatigue are limited to static conditions. It is then necessary the development of new techniques to detect the occurrence of the phenomenon of fatigue in dynamic conditions similar to those existing in the daily life.