The general objective of the study is to determine the effectiveness on local mechanical hypoalgesia, pain intensity, disability and psychological variables of the deep dry needling technique on a latent trigger point of the upper trapezius muscle.

The specific objective of the study is to observe the interaction between patient expectations and hypoalgesic effects in patients who will receive the same technique but with different explanations about it before punction and which could influence on the modulation of post-punction pain.

Study design:

A randomized, longitudinal, experimental, prospective, parallel and double-blind clinical trial was conducted, where both the study subject and the researcher performing the measurements do not know which treatment group they belong to.

Participants The sample was composed of 42 healthy patients residing in the Community of Madrid, all of whom were recruited personally for the study. All of them will have 15 incisions by dry needling in latent trigger point of the upper trapezium localized by palpation. All patients will read the information sheet explaining what the study will consist, as well as the informed consent form, which they will sign voluntarily beforehand. Patients were randomly assigned using GraphPad Software's QuickCals application (La Joya, CA, USA) to one of the 3 study groups.

Each group will be given a different sentence: one group will be attempted to influence with positive expectation, another with neutral expectation, and yet another will be attempted to influence with negative expectation.

Measurement instruments

Measurement of the range of movement by means of an inclinometer. To measure the range of movement the patient will be seated in a chair; feet supported on the floor, triple flexion of lower limbs of 90º (hip, knee and foot), back well supported and straight, head straight and look at the horizon. The inclinometer will be positioned to measure flexion, extension, right and left tilt and right and left rotation. The inclinometer for CROM (cervical range of motion) is approved and validated in different studies.

Measurement of pain threshold to pressure

A digital algometer was used to measure mechanical hyperalgesia. The model used was the X® brand, consisting of a 1 cm2 cylindrical rubber attached to a pressure gauge. It is calibrated in kilograms (kg) and pounds. The scale expressed in kg/cm2 was used. All patients were familiarized with this test through a trial session. They were instructed to say STOP when the pressure sensation changed to painful. Three perpendicular measurements were made on an active or latent myofascial trigger point situated in upper trapezium muscle, the mean was calculated and the data were recorded for analysis. A rest period of 30 seconds was established between the measurements. A dermographic pencil was used to mark these points prior to measurement. The intra-assay reliability is high in the upper trapezius muscle (ICC = 0.94-0.97). The minimum detectable change (CMD) for considering the results as clinically relevant in the upper trapezius fibres has been shown to be between 0.45 kgf and 1.13 kgf.

Procedural protocol

Prior to the technique, the patient will be explained that the study seeks to observe if pain appears after the dry needling procedure. During the explanation, the desired expectation will be introduced:

• Group with positive expectation: "it is a very effective technique that achieves excellent results in the improvement of the cervical musculature"
• Group with neutral expectations: "It's a physical therapy technique used to treat neck pain and we're investigating its effects"
• Group with negative expectation: "this is a technique that will cause discomfort in the area of intervention of the cervical muscles after applying it ".

Inclusion Criteria:

• Be between 18 and X years of age.
• Presence of at least one latent myofascial trigger point in the upper trapezius muscle.
• Patients who speak and understand Spanish correctly.
• Subjects without previous experience in dry puncture treatment.

Exclusion Criteria:

• If patients had neurological signs and symptoms.
• Subjects with a history of trauma, fracture or previous spinal surgery.
• Subjects with a history of musculoskeletal and/or rheumatological diseases.
• Unsurpassed fear of needles
• Coagulation disorders
• Infiltration of corticosteroids or local anesthetics for one year prior to the study.
• Taking analgesic or anti-inflammatory medication the week before the study.

Before the treatment, it will be explained to the patient that the study seeks to observe if pain appears after the dry needling. During the explanation, the desired expectation will be introduced:

• Group with positive expectation: "it is a very effective technique that achieves excellent results in the improvement of the cervical musculature"
• Group with neutral expectations: "It's a physical therapy technique used to treat neck pain and we're investigating its effects"
• Group with negative expectation: "this is a technique that will cause discomfort in the area of intervention of the cervical muscles after applying it ".

Neither the subjects assigned to the groups nor the researchers who measured the variables knew which group they belonged to.

Patients will be randomly assigned through GraphPad Software's QuickCals application (La Joya, CA, USA) to one of the 3 study groups.