The main objective:

To compare the effect on muscle tone between the application of digital capacitive diathermy and the application of ultrasound on the myofascial trigger points (MTP) of the upper trapezius muscle.

Hypothesis:

The application of digital capacitive diathermy on myofascial trigger points of the trapezius muscle compared to the application of ultrasound produces objective changes in muscle tone, and this change is superior to the changes generated by the US.

It is a simple-blinded randomized crossover clinical trial where volunteer subjects, older than 18 years, have a latent or active proximal MTP1 (intermediate part of the anterior margin of the upper part of the muscle near the vertical fibers of the muscle attached to clavicle) in the upper trapezius.

It will assess if there are changes in the muscle tone of the trapezius muscle after applying digital capacitive diathermy (DCD) or ultrasound (US) in the latent or active MTP1 of the trapezius muscle in healthy adults.

Each patient will receive a single session of each treatment in the affected trapezius. The order in which treatments are received - US followed by digital capacitive diathermy, or vice versa - is determined at random.

To remove any carryover of effects, there will be a week of washing period between the two interventions.

Intervention:

- DCD: The patient is positioned in prone position on stretcher. Firstly, it will apply almonds oil on the MTP1 of the upper trapezius affected. Then, it will put the "musculotendinous injury FAST" program which lasts 6 minutes; and, it will move the ultrasound applicator in contact with the skin with a velocity approximately between 2.5 and 4 centimeters per second.

- US: The patient is positioned in prone position on the stretcher. Firstly, it will select parameters (frequency: 1MHz, intensity: 1.0 W/cm2, mode: continuous). Then it will apply a slow technique of circular movements with a speed of approximately between 2.5 and 4 centimeters per second over the area of the MTP1 of the upper trapezius affected during 6 minutes.

Assessment:

To assess the effectiveness of these techniques, several tests will be performed on the subjects:

• Myotonometric measurements using a myotonometer to obtain frequency, decrement (elasticity) and stiffness of the evaluated points and MTPs.
• Algometry results will bring information of the PPT of evaluated MTPs.
• The 0-10 Numeric Pain Rating Scale results will bring information of the subjective dolor perception of the subjects.
• Inclinometer results will bring information of the ROM of cervical spine lateral inclination.
• The Neck Disability Index results will provide information on how much neck pain interferes in the daily activities of patients.

Inclusion Criteria:

• Older than 18 years

• Presence of an active or latent MTrP 1 in the upper trapezius:

  • Presence of taut band in a skeletal muscle.
  • Presence of a hypersensitive point in the taut band.
  • Local twitch response caused by palpation of the taut band.
  • Reproduction of the typical referred pain pattern of MTrPs in response to compression.
  • Spontaneous presence of the typical pain pattern and/or patient's recognition of that pain as familiar (criteria only applicable to the active MTrPs).

Exclusion Criteria:

• History of neurological disorders (radiculopathy).
• Cervical surgery.
• Chronic pain in any part of the body as a result of a traumatic incident.
• Chronic rheumatic disease.
• Medical diagnosis of fibromyalgia.
• Systemic diseases.
• Actual pregnancy.
• Clinical depression.
• Body mass index ≥30.
• To receive treatment of myofascial syndrome in the muscles of the cervico-dorsal area (physical therapy, invasive techniques ...) during the month prior to the beginning of the study.
• Ingestion of medication (analgesics, muscle relaxants, psychotropic or anti-inflammatory agents) in the three days prior to the start of the study.

Exit criteria:

• Patient´s petition.
• Appearance of any lesion that might contraindicate the use of electrotherapy techniques.