The same procedure will be performed as in the experimental treatment, but in this case, the electric current will be placebo and only the first 15 seconds will slightly notice it. This will add to a protocol of motor control exercises for deep abdominal and lumbar muscles.

Transcutaneous electrical nerve stimulation will be applied through 4 patches / adhesives placed in your lower back for 30 minutes. This will add to a protocol of motor control exercises for deep abdominal and lumbar muscles.

The same procedure will be performed as in the experimental treatment, but in this case, the needle will not be inserted and the electric current will be placebo and only the first 15 seconds will slightly notice it. This will add to a protocol of motor control exercises for deep abdominal and lumbar muscles.

Ten consecutives pressure pain stimulus will be conducted, pain intensity in the first, fifth and tenth will be asked. The difference from 1 to 10 will be the value that reports on the state of excitability of the posterior horn of the medulla

First, pressure pain stimulus (test stimulus) will be conducted in the distal phalanx of the thumb. Second, occlusion cuff will be inflated around the arm of patient until the patient feeling a painful intensity (conditioned stimulus) of 6/10. Finally, after 30 seconds the stimulus will be done. The difference in the mean value of the initial algometry with the mean value of algometry during the conditioning stimulus will indicate the state of the descending pain inhibitory system.

The scale assesses two dimensions: the intensity of pain and pain related to disability. It can be used in any chronic pathology including musculoskeletal problems and low back pain. It allows the graduation of the severity of chronic pain and the subsequent analysis of the qualitative changes for that pain. The scale has 7 items, which are of the Likert type of 11 points, with a total range of 0 to 70 points.

The Oswestry Disability Index (ODI) is a validated, self-reported instrument used by clinicians and researchers to quantify disability for low back pain.

The self-completed questionnaire contains ten topics concerning intensity of pain, lifting, ability to care for oneself, ability to walk, ability to sit, sexual function, ability to stand, social life, sleep quality, and ability to travel. Each topic category is followed by 6 statements describing different potential scenarios in the patient's life relating to the topic. The patient then checks the statement which most closely resembles their situation. Each question is scored on a scale of 0-5 with the first statement being zero and indicating the least amount of disability and the last statement is scored 5 indicating most severe disability. The scores for all questions answered are summed, then multiplied by two to obtain the index (range 0 to 100). Zero is equated with no disability and 100 is the maximum disability possible.

The SF-12 is a validated, health-related quality-of-life questionnaire consisting of twelve questions that measure eight health domains to assess physical and mental health. Physical health-related domains include General Health (GH), Physical Functioning (PF), Role Physical (RP), and Body Pain (BP). Mental health-related scales include Vitality (VT), Social Functioning (SF), Role Emotional (RE), and Mental Health (MH). The instrument has been validated across a number of chronic diseases and conditions. The response options of the SF-12 v2 form Likert-type scales that evaluate intensity or frequency. The number of answer options ranges from three to six, depending on the item, and each question is given a value which is then transformed into a scale from 0 to 100.

Tampa Scale for Kinesiophobia. To assess the fear of movement and pain-related fear. The 11 items are scored 1-4, with total scores ranging from 11 to 44. The addition of all the points obtained from each of the items results in the level of kinesiophobia, with higher scores indicating greater perceived kinesiophobia

Pain Catastrophizing Scale (PCS). This tool is a 13-item questionnaire designed to measure the three components of pain-related catastrophizing: rumination, magnification, and helplessness, resulting in a unique score. Each item is responded to on a 5-point scale (0 not at all, 4 all the time) relating the degree to which the individual experiences a thought or feeling of a painful situation.

The Becks Depression Inventory-II is a validated, self-administered questionnaire consisting of 21 multiple choice questions. It is one of the most commonly used instruments to measure the severity of a depression. Possible scores range from 0 (no depression) to 63 (severe depression).

The state-trait anxiety inventory (STAI) is a questionnaire that measures trait anxiety (a personality factor that predisposes the patient to suffer from anxiety) and the state of anxiety (environmental factors that protect or generate anxiety). Each of the two sub-scales (trait anxiety and state anxiety) consists of 20 items, ranging from 0 (nothing) to 3 (a lot).

Global Rating of Change (GRoC) scales provide a means of measuring self-perceived change in health status. Possible scores range from -5 (very much worse), through 0 (unchanged) to +5 (completely recovered).

The patients of the sham groups will be asked after the interventions of PNMES if they belonged to the group of deep electro-stimulation, being able to content: Sure that yes, moderately that yes, I do not know, moderately that no or sure that no.

The Spanish version of the Central Sensitisation Inventory will be used to identify symptoms related to central sensitisation. It is a self-report questionnaire that assesses a total of 25 sensitisation-associated symptoms on a 5-point Likert scale. The total score ranges from 0 to 100, where >40/100 points suggest the presence of sensitisation-associated symptoms. It has been found to have high reliability and validity.