For the assessment of general health status, the "SF-36" health status questionnaire will be used. The SF-36 health questionnaire is a widely used outcome instrument to assess health-related quality of life. It is a generic multidimensional instrument validated for several pathologies. The physical component summary of the SF36 assesses functional capacity, physical aspects, pain and general health, while its mental component summary assesses vitality, social functioning, emotional aspects and mental health.

The SWLS is a useful instrument for academic research in social, medical and other disciplines, as it has demonstrated a high degree of reliability in several studies, appropriate internal consistency among items, correlations between items and adequate validity. The instrument consists of a brief 5-question questionnaire designed to evaluate people's general satisfaction with their lives. It requires approximately one to five minutes of the respondent's time to complete. Responses are recorded on a 7-point Likert rating scale, where 1 represents "strongly disagree" and 7 means "strongly agree". Scores obtained can range from 5 to 35, with higher scores indicating that the person perceives that important areas of his or her life are going well, while lower scores indicate the opposite.

The PSS is a scale designed to measure the degree to which individuals rate situations in their lives as stressful. The items assess the degree to which people consider life to be unpredictable, uncontrollable, or overloaded, central components of stress. The scale includes questions designed to assess the current level of stress experienced by the subject. It is a brief scale, consisting of only 14 items, takes only a few minutes to administer, and is easily scored.

The HADS will be used to assess anxiety and depression symptoms. The HADS is a brief two-dimensional self-completed questionnaire designed to assess anxiety and depression symptoms in individuals with physical health problems. It consists of 14 items, 7 of which focus on anxiety symptoms and the other 7 on depressive symptoms. The HADS is considered a valuable tool for screening for these psychological problems in medical settings because of its brevity, ease of administration, and good psychometric properties.

The Oswestry Low Back Pain Disability Scale will be used to assess the level of disability due to pain. This scale is the most widely used, together with the Roland-Morris scale, in the evaluation of the patient with low back pain to measure its functional repercussion on activities of daily living. It is made up of ten items related to activities of daily living. For each item there are 6 possible answers ranging from no disability [0] to total disability [5]. The Spanish version, which has been translated and culturally adapted, was used.

A digital algometer (Model FXD 10, Wagner Instruments, Greewich, CT, USA) that measures pressure in kg/cm2 will be used to assess the PPT. The UDP is defined as the minimum pressure necessary for the pressure sensation to begin to be perceived as painful. To assess it, increasing pressure is applied to the upper portion of the trapezius muscle on the right side at a rate of one kilogram per second until the subject indicates that the sensation begins to be painful. The study subject was in a seated position. To improve accuracy, the investigator in charge of taking this measurement precisely marked the area where the measurement would be taken with a marker. Each measurement would be taken three times and the arithmetic mean was taken to establish the final value collected. Subsequently, it was evaluated in the left upper trapezius muscle, in the right quadratus lumborum muscle and in the left quadratus lumborum muscle, following the procedure previously described.

For the assessment of hamstring extensibility, angular tests and a linear test will be performed. As a reference angular test, the straight leg raising test will be performed, assessing both legs passively (EPRPassive) and actively (EPRActive). The measurement will be performed with an inclinometer (Baseline, model Bubble ® inclinometer, White Plains, NY 10602 (USA). The sit-and-reach test will also be performed, assessing both the pelvic tilt (with the inclinometer) and the distance reached in the test (linear measurement). The tests will be performed in a randomized order and by the same investigator for each test.

For the assessment of lumbar spine flexibility, the Modified-Modified Schober Test will be performed. The examiner places the thumbs on the lower margin of the subject's upper posterior spines. An ink mark is drawn along the midline of the lumbar spine horizontal to the spines. While the examiner holds the tape measure firmly against the subject's skin, he or she marks a second line 15 cm above the original (upper mark). The subject is then asked to perform active anterior trunk flexion without increasing pain. The new distance between the lower and upper marks is measured. The subject returns to the neutral position. The difference in the initial distance between the marks in the neutral position and the new measurements taken in the flexion position is used to indicate the amount of lumbar flexion. After each measurement, the skin marks are removed with alcohol.