ELECTRO MUSCLE STIMULATION
Electrostimulation is a technique which, by means of electric pulses that act on the muscle’s motor points (motoneuron), causes muscular contraction responses similar to voluntary contractions (exercise).
Most of human body muscles belong to the striated or voluntary muscle category, with approximately 200 muscles on each side of the body (about 400 in all).
The physiology of muscular contraction
The skeletal muscle performs its functions by way of a contraction mechanism.
When a person decides to make a movement, the motor center of the brain sends an electric signal to the muscle that is to contract.
When the signal reaches the muscle, the motor plate of the muscle surface produces the depolarization of the muscle membrane and the release of CA++ ions inside it. The Ca++ ions, interacting with the actin and
myosin molecules, activate the contraction mechanism which results in the shortening of the muscle.
The amount of energy needed for this contraction is provided by the adenosine triphosphate (ATP) and is sustained by an energy recharging system based on aerobic and anaerobic energy mechanisms which consume carbohydrates and fat. In other words, electric stimulation is not a direct source of energy but functions as a tool to set off a muscular contraction.
The same type of mechanism is activated when the muscular contraction is set off by the electro muscle stimulator (EMS). They carry out the same function as an impulse naturally transmitted by the motor nervous system.
When the contraction is over, the muscle relaxes and returns to its original state.
Isotonic and isometric contractions
An isotonic contraction manifests itself when, during a movement, the interested muscles exceed resistance from the outside by shortening, thus provoking a constant state of tension in the ends of the tendons. When
outside resistance impedes its movement, the muscular contraction, instead of provoking a shortening effect, brings about an increase in the tension at the extremes; this is called isometric contraction. In the case of electro stimulation normally a stimulation for isometric conditions is used, due to its ability to provoke a more powerful and efficient contraction.
The distribution of different types of fibers in the muscle
The ratio between the two main categories (type I and type II) can vary noticeably.
There are muscle groups which are typically made up of type I fibers, like the soleus, and muscles which are made up of only type II fibers, like the orbicular muscle. However, on the whole, the muscles in the human body are composed of a combination of the two types.
Studies on the distribution of fibers in the muscle mass have highlighted the close relationship between the (tonic or phasic) motoneuron and the functional characteristics of the fibers it innervates and have shown that a specific (particularly sports) motor action can bring about a functional adaptation of fibers and a change in their metabolic characteristics.
Type of motor unit Type of contraction Contraction frequency
Tonic ST Slow contraction I 0 – 50 Hz
Phasic FT Fast contraction II 50 – 70 Hz
Phasic FTb Fast contraction II b 80 – 120 Hz
Electrostimulation, thanks to its ability to stimulate with specific frequencies, lets you train specifically those fibers which intervene in the movement you want to train (rapid fibers for explosive movements, slow fibers for long-lasting action) or to transform the metabolism and characteristics of intermediate fibers in order to make them more suitable to carry out the desired movement.