Achilles tendinopathy is characterized by pain, decreased performance and swelling in and around the tendon. Up to 29% of patients with Achilles tendinopathy may require surgical intervention. It can be complicated by partial tears or complete rupture, placing a long-term burden on the healthcare system and making treatment more difficult.

The most common location of Achilles tendinopathy is in the insertional area of the calcaneus, 1.5 to 2 cm cranial to the bone. The most common location of pathologic inflammation was at the fascial intersection of the medial gastrocnemius and soleus when fused with the proximal Achilles tendon (66% of patients and the distal part of the Achilles tendon near the calcaneus. The four cornerstones of tendon histopathology are: cellular activation and increased cell number, increased ground substance, collagen disorganization and neovascularization. In addition, blood supply is one of the most influential factors in tendon tissue repair. A recent clinical trial compared the outcome after low frequency microwave hyperthermia with traditional ultrasound. The hyperthermia group recorded significantly better results after treatment and one month later. The use of deep heating modalities, due to their beneficial effects of increased circulation and cellular metabolism resulting in increased waste and nutrient exchange in a specific area, has long been accepted as part of the treatment of overuse tendinopathies . The application of heat has been reported to improve blood flow and oxygen saturation in the Achilles tendon.Physical therapies based on electrical or electromagnetic stimulation have been used in rehabilitation, in some cases combining electrical therapy with radiofrequency. Specifically, resistive capacitive electrical transfer therapy (CRet) has been used in physical rehabilitation and sports medicine to treat muscle, bone, ligament and tendon injuries. CRet is a non-invasive electrothermal therapy classified as deep thermotherapy, which is based on the application of electrical currents within the radiofrequency range of 300 kHz - 1.2 MHz. he effects attributed to this technique include increased deep and superficial blood circulation, vasodilatation, increased temperature, elimination of excess fluid and increased cell proliferation. Some of these reactions, such as increased blood perfusion, are known to be related to the increase in temperature, but others, such as increased cell proliferation, appear to be primarily related to the passage of current. There are currently numerous treatment proposals for this pathology, however, the only one that has shown significant improvements are eccentric exercise protocols. The only drawback of this type of exercise is that the results are obtained in the long term.

There is currently no study that has compared the effectiveness of adding a tecartherapy protocol to the eccentric exercise protocol in chronic Achilles tendinopathy in athletes in the short and medium term in both functional and structural variables.

Achilles tendinopathy is characterized by pain, decreased performance and swelling in and around the tendon. Up to 29% of patients with Achilles tendinopathy may require surgical intervention. It can be complicated by partial tears or complete rupture, placing a long-term burden on the healthcare system and making treatment more difficult.

The most common location of Achilles tendinopathy is in the insertional area of the calcaneus, 1.5 to 2 cm cranial to the bone. The most common location of pathologic inflammation was at the fascial intersection of the medial gastrocnemius and soleus when fused with the proximal Achilles tendon (66% of patients and the distal part of the Achilles tendon near the calcaneus. The four cornerstones of tendon histopathology are: cellular activation and increased cell number, increased ground substance, collagen disorganization and neovascularization. In addition, blood supply is one of the most influential factors in tendon tissue repair. There is an animal study in which when the blood supply to the Achilles tendon of a rabbit was decreased, the following changes were observed: the normally attached fascicles of the rabbit tendon separated and the tenocytes became disorganized from the interfascicular spaces. Collagen filaments became acellular and fragmented. Furthermore, it was shown that the changes observed in chronic degenerative tendon disorders in humans are the same as those that occur when the blood supply to the rabbit Achilles tendon is disturbed. This demonstrates that vascular supply is one of the important factors in treating tendon tissue.

A recent clinical trial compared the outcome after low frequency microwave hyperthermia with traditional ultrasound. The hyperthermia group recorded significantly better results after treatment and one month later. The use of deep heating modalities, due to their beneficial effects of increased circulation and cellular metabolism resulting in increased waste and nutrient exchange in a specific area, has long been accepted as part of the treatment of overuse tendinopathies . The application of heat has been reported to improve blood flow and oxygen saturation in the Achilles tendon. Thus, thermal agents may be an effective method to treat this type of tendon disorders.

Physical therapies based on electrical or electromagnetic stimulation have been used in rehabilitation, in some cases combining electrical therapy with radiofrequency. Specifically, resistive capacitive electrical transfer therapy (CRet) has been used in physical rehabilitation and sports medicine to treat muscle, bone, ligament and tendon injuries. CRet is a non-invasive electrothermal therapy classified as deep thermotherapy, which is based on the application of electrical currents within the radiofrequency range of 300 kHz - 1.2 MHz. While the heat conducted by surface thermotherapy cannot reach the muscle due to the electrical resistance of the tissues, the capacitive-resistive electric currents in CRet therapy can generate heating of deep muscle tissues, which in turn improves hemoglobin saturation. In Europe, CRet is widely used in various medical rehabilitation processes. The physiological effects of this type of physiotherapy are generated by the application to the human body of an electromagnetic field with a frequency of approximately 0.5 MHz. The effects attributed to this technique include increased deep and superficial blood circulation, vasodilatation, increased temperature, elimination of excess fluid and increased cell proliferation.

Some of these reactions, such as increased blood perfusion, are known to be related to the increase in temperature, but others, such as increased cell proliferation, appear to be primarily related to the passage of current.

It is also true that this increase in tissue temperature, generated through the application of the device, is a physical reaction to the passage of the current (Joule effect). Although there are already clinical publications that support this mechanism, the amount of energy and current that must be transferred to obtain the desired temperature increase is unknown. Moreover, the control of these reactions, by adjusting parameters such as absorbed power and electrode position, are still largely based on the empirical experience of therapists.

Recently, new cadaveric publications have been published that support the mechanisms of current flow and thermal changes in this situation, especially a study by López-de-Celis et al. in which the thermal effects and current flow in the myotendinous junction of the medial gastrocnemius and Achilles tendon were demonstrated.

With this background, in which thermal effects, current passage and symptomatic improvements have been demonstrated in patients with pathology, the possibility that these treatments improve functional sports capabilities is raised. This hypothesis arises from the fact that the passage of current and thermal changes have been directly related to viscoelastic changes in capsular and muscular tissue. There are currently numerous treatment proposals for this pathology, however, the only one that has shown significant improvements are eccentric exercise protocols. The only drawback of this type of exercise is that the results are obtained in the long term.

There is currently no study that has compared the effectiveness of adding a tecartherapy protocol to the eccentric exercise protocol in chronic Achilles tendinopathy in athletes in the short and medium term in both functional and structural variables.

Recently, new cadaveric publications have been published that support the mechanisms of current flow and thermal changes in this situation, especially a study by López-de-Celis et al. in which the thermal effects and current flow in the myotendinous junction of the medial gastrocnemius and Achilles tendon were demonstrated.

With this background, in which thermal effects, current passage and symptomatic improvements have been demonstrated in patients with pathology, the possibility that these treatments improve functional sports capabilities is raised. This hypothesis arises from the fact that the passage of current and thermal changes have been directly related to viscoelastic changes in capsular and muscular tissue. There are currently numerous treatment proposals for this pathology, however, the only one that has shown significant improvements are eccentric exercise protocols. The only drawback of this type of exercise is that the results are obtained in the long term.

There is currently no study that has compared the effectiveness of adding a tecartherapy protocol to the eccentric exercise protocol in chronic Achilles tendinopathy in athletes in the short and medium term in both functional and structural variables.

Inclusion Criteria:

• Study participants must have signed the informed consent form in order to evaluate their participation in the study.
• Actively practice some sporting activity.
• Have a medical diagnosis of chronic Achilles tendinopathy of more than 3 months of evolution.
• Not having previously received any tecartherapy treatment.
• Be over 18 years of age.

Exclusion Criteria:

• Volunteers who have suffered a sports injury during the last two months or are unable to perform physical activity.
• Subjects with bilateral tendinopathies.
• Subjects who report allergies to the conductive cream.
• Not understanding the information provided by the therapist.
• Participating in other research studies.
• Subjects undergoing pharmacological medical treatment that may interfere with the measurements, such as treatment with anticonvulsants, antidepressants.