Electroanalgesia therapy and the McKenzie exercise protocol will be applied by six therapists with more than 10 years of experience in both procedures. This program will be developed in the Health Sciences clinical units of the Universities of Almeria, Granada and Malaga.

The SF-36 quality of life questionnaire assesses 8 domains including physical functioning, physical role, bodily pain, general health, vitality, social functioning, role-emotional, and mental health. Scores range from 0 to 100% (with higher scores indicating greater health), reflecting the individual's self-perceived health-related quality of life.

The Pittsburgh Quality of Sleep Questionnaire Index (PSQI) will be used to study the quality of sleep. It comprises 24 items where the subjects respond to 19 of these items, and individual living in the same dwelling (or hospital room) responds to the remaining 5. Scores are obtained on each of 7 components of sleep quality: subjective quality, sleep latency, sleep duration, habitual sleep efficacy, sleep perturbations, use of hypnotic medication, and daily dysfunction. Using a four-point, Likert-type scale, respondents indicate how frequently they exhibit certain sleep behaviors (0 = "few," 1 = "sometimes," 2 = "often," and 3 = "almost always"). Scores on items belong to factors 2 and 5 (restoration after sleep and satisfaction with sleep) and are reversed before being tallied. Total scores can range from 0 to 84, with higher scores demoting more acute sleep problems.

The 17-item Tampa scale for kinesiophobia assesses fear of movement or of injury or reinjury. Participants rate their beliefs regarding kinesiophobia on a 4-point Likert scale, ranging from "strongly disagree" to "strongly agree".

The Pain Catastrophizing Scale (PCS) is a self-assessment questionnaire to examine catastrophizing in clinical and nonclinical populations. Catastrophizing is commonly described as an exaggerated negative orientation toward noxious stimuli and plays an important role in experiencing and coping with pain. The PCS consists of 13 statements containing a number of thoughts and feelings one may experience when having pain. The items are divided into the categories of rumination, magnification and helplessness, with each item scored on a 5-point scale. The PCS consists of 13 statements containing several thoughts and feelings one may experience when having pain.

Cervical range of motion is assessed with the patient sitting comfortably on a chair, with both feet flat on the floor, hips and knees at 90º of flexion, and buttocks positioned against the back of the chair.

The investigators will measure the maximum isometric strength of the neck extensor muscles using a hand-held dynamometer (HHD). The patient will remain seated in a chair, with their feet flat on the floor, their hips and knees at 90º of flexion and the neck in the anatomical position, the patient will hold the HHD with both hands resting on their occiput, opposing the extension, and will be asked to perform a progressive isometric cervical extension for 3 seconds until reaching their maximum level of strength.

To measure the isometric endurance of the neck flexors, the investigators will place the patient in a supine position and ask him/her to perform a double chin tuck, which he/she must maintain throughout the test. While maintaining this position, he/she must flex his/her neck until his/her head is 2.5 cm off the table and maintain this position for as long as possible. The evaluator will time the duration of the test, which will be terminated if the patient loses the position for more than one second or asks to end due to fatigue or pain.