Summary
Highlights
Electrostimulation involves introducing action potentials into muscle and nerve fibers using electrical currents. These currents trigger an impulse that leads to muscle contraction or nerve excitation. The currents used are usually interrupted galvanic currents, which are low-frequency (between 1 and 1000 Hz, specifically below 500 Hz for production) and include an electrical silence period to respect the refractory period of muscle and nerve fibers, resulting in sustained muscle contraction.
Various types of pulses are used, including square or rectangular, triangular (with linear progressive, exponential progressive, or linear progressive ascent and descent forms), faradic (with a positive triangular phase for ascending/descending and a negative phase), and those generated by capacitor discharges. More recently, microelectronics offer rectangular, square, biphasic symmetric, and asymmetric currents. Other types include exponential, faradic with abrupt fall, and sinusoidal (less frequently used) pulses.
Electrostimulation serves three main purposes: prevention, diagnosis, and treatment. For prevention, it helps maintain muscle trophic state and good condition, preventing atrophy in cases of potential pathology. For diagnosis, it helps differentiate between innervated and denervated muscle fibers, which is crucial for appropriate treatment planning. For treatment, it addresses established pathologies like muscle atrophy or denervation, with the specific electrical therapy depending on the muscle's characteristics and innervation degree.
The neurophysiological fundamentals of electrostimulation aim to achieve muscle contraction by considering motor unit types, number, discharge frequency, and contraction speed. Skeletal muscle fibers are classified into Type 1 (slow-twitch oxidative, found in postural muscles, non-mutating) and Type 2 (fast-twitch, sub-classified into 2a and 2b). Type 2a fibers are oxidative and glycolytic, using an anaerobic energy system, while Type 2b are pure glycolytic and entirely anaerobic, suited for short-duration rapid work. There are also transitional fibers that can change from rapid to slow, but not vice-versa.
In voluntary muscle contraction, slow-twitch fibers are recruited first, followed by fast-twitch fibers. However, with electrostimulation, this order is reversed: fast-twitch fibers are recruited first, followed by slow-twitch fibers. This inversion explains why patients often experience greater fatigue after electrostimulation compared to normal physical activity, as the more fatigue-prone fast-twitch fibers are activated preferentially.