**5. Capacitive and resistive electrodes**

The capacitive electrode is covered by an insulator. Imagine a capacitor formed on one side by the capacitive electrode, and on the other, a resistive conductor formed by the biological tissue and another metallic conductor (return plate) that closes the circuit. The capacitive conductor is made up of metal compounds and alloys. The application of a capacitive conductor is characterized by displacement currents instead of conduction, and the charged particles tend to have a higher charge density in the vicinity of the dielectric, act on the most superficial tissues (first 3 cm) rich in water and its energy tends to progressively increase from the return plate to the capacitive electrode with the consequent increase in temperature of the tissues.

In resistive mode, the electrode is conductive, metallic and is applied directly to the body. The current passes through the sector of the body where it is applied, dispersing towards the return electrode. During this process, heat is generated due to the energy delivery in the tissue and the resistance that the tissues oppose to its passage. The concentration of charges, and therefore the biological effect, occurs at the points of greatest resistance of the current, such as the bone tissue, which is located between the active electrode and the return electrode. But other highly resistant tissues due to their low water content such as tendons, ligaments and bands of muscles and tendons will have also biological effect. In this way, a charge displacement current is created within the biological tissue that determines the involvement of the deep layers and the consequent homogeneity of the endothermic response with greater depth. The plate electrodes are 200 m<sup>2</sup> capacitive electrodes (**Figure 2**).

The more area of application, the more energy is delivered. A larger area allows the penetration of the energy to be more extensive and the effects more extensive in the area of the injury and the surrounding tissues.

**Figure 2.** *Electrodes, resistive (a) capacitive (b) and capacitive plate of 200 cm2*

### **6. Energy channels**

Being able to increase the amount of energy by incorporating more channels to the treatment, first of all allows incorporating a larger area of application, covering more space around the lesion, and can be used simultaneously with physical activity, on the one hand. Moreover, the.

*.*

capacitive and resistive electrode can also be used simultaneously. An energy summation occurs where in the most superficial area the energy load is greater.

### **7. Thermal and athermal effects**

Heat is generated in the tissue both by the electrical process and by the magnetic field. The static magnetic field cannot heat the human body as it does not transfer any net energy, so it does not produce heat. Therefore, the tissue heating mechanism is by electric current and is based on the generation of joules of heat. The heat generated is described by Joule's Law:

$$\mathbf{E} = \frac{\mathbf{j}^2}{\sigma} \tag{1}$$

Where E is the energy, j is the density of the electric current and σ is the electrical conductivity. The conductivity is 1 / R (R = resistance).

The absorption of electromagnetic energy by the tissues of the human body is complicated because there are different types of tissues, with different coefficients of conductivity. As the depth of penetration into the tissues increases, the frequencies change, such that most of the incident energy can be transmitted at one frequency, but absorbed at another. The depth of penetration per frequency depends on several factors: dry skin, infiltrated fat, and muscle, calculated according to the characteristics of the Gabriel model.

All mechanisms that cannot induce a temperature increase greater than 0.010 ° C (when we consider a system as a living organism), less than 0.001 ° C (when a system is considered as a cell), or again less than 0.0005 °C are considered nonthermal, when studying a sub-cellular system.

At present, there is a controversy between the thermal sensation of the patient and the application of energy. Hence the term athermic, as the temperature in the tissue does not increase. The real connotation of athermic is that the patient does not perceive the increase in temperature. The patient has little thermal

*Use of an Evolution in Tecartherapy for Muscle Improvement and Treatment of Sports Injuries DOI: http://dx.doi.org/10.5772/intechopen.96776*

sensation, since it is an application with little energy. Due to the fact that energy is introduced into the tissue, it causes the water molecules to vibrate and this produces heat.
