Effects of a Hip Flexor and Extensor Muscle Training Program in Individuals with Chronic Mechanical Low Back Pain

Range of motion of the hip flexors will be assessed using the Modified Thomas Test, also recording the body area where the sensation of stretch is felt, as well as the intensity.

Range of motion of the hip flexors will be assessed using The modified Ober test, also recording the body area where the sensation of tension or stretch is felt, as well as the intensity.

Low back pain will be assessed using a visual analog scale (VAS). Information on average pain over the last 3 days, the maximum pain experienced, and the current pain level will be collected. The patient will mark their pain level with a line on scale ranging from 0 to 100 millimeters, where "0" represents no pain and "100" represents the worst imaginable pain, in relation to daytime pain (average VAS perceived over the last 3 days and at the present moment). Additionally, patients will be asked about the location and intensity of other symptoms using a Likert scale and a body map.

It is a questionnaire composed of 10 categories: (1) pain intensity, (2) self-care, (3) lifting objects, (4) walking, (5) sitting, (6) standing, (7) sleeping, (8) sexual life, (9) social life, and (10) traveling. Each category consists of 6 items scored from 0 to 5, with a score of 0 on the first statement and 5 on the last. A mark at the highest levels indicates that the person is in worse condition. The questionnaire includes an additional question about previous treatments. If more than one response is selected, the highest score is considered. If all 10 sections are completed, the score is calculated as follows: the maximum score for the 10 sections is 50 points. If all sections are completed, this number is converted into a percentage with a total of 100. The Spanish version of the questionnaire shows good reliability and validity with an ICC between 0.89-0.97 and was validated in Spanish.

The pelvic movement will be recorded in video format in the sagittal plane for each patient in both standing and sitting positions with 45° of hip flexion. In each measurement it will be registered the range of movemento of the pelvis. The movement consist of the total range of anterior and posterior rotation of the pelvis.

Pain during pelvic tilting will be assessed using a visual analog scale (VAS). The patient will mark their pain level with a line on scale ranging from 0 to 100 millimeters, where "0" represents no pain and "100" represents the worst imaginable pain. Additionally, patients will be asked about the location using a a body map and also the movement phase where the pain appears or is at its worst.

A maximum voluntary isometric contraction (MVIC) test will be performed for the biceps femoris, gluteus maximus and tensor fasciae latae using a load cell.

To assess dynamic activation, a gait test will be used. The gait test will involve walking on a treadmill for one minute at a comfortable speed, chosen by each patient. Two repetitions will be performed. Additionally, each subject will have an adaptation period to ensure they feel comfortable during the test.

To assess activation, internal oblique, lumbar multifidus, gluteus maximus, and tensor fasciae lataewill be recorded simultaneously.

The total percentage of activation for each muscle during the central 30 seconds of the test will be calculated.

In addition, the speed achieved by each participant will also be recorded.

Weight in kq using the Tanita TBF-300, Amsterdam, Belgium

The MOS Sleep Scale (Sleep Scale from the Medical Outcomes Study) will be used, which has proven to be a valid and reliable tool.

The Tampa Scale for Kinesiophobia-11 (TSK-11) is a self-administered questionnaire recommended by the clinical guidelines for neuropathic pain assessment to measure fear of movement. It consists of 11 items assessing two factors: Activity Avoidance and Fear of Harm. Each item is rated on a 4-point Likert scale ranging from strongly disagree to strongly agree. High scores indicate a greater degree of kinesiophobia.

This instrument measures symptoms related to central sensitization syndromes. Part A assesses 25 common symptoms related to central sensitization syndromes, with a total score ranging from 0 to 100. Part B (not scored) asks if the participant has been diagnosed with one or more specific conditions, including seven different central sensitization syndromes.

The PCS is a 13-item self-administered scale and one of the most widely used to assess pain catastrophizing. It comprises three dimensions: a) rumination, b) magnification, and c) helplessness. The theoretical range of the scale is between 13 and 62, with lower scores indicating low catastrophizing and higher scores indicating severe catastrophizing.

These charts assess health-related quality of life or perceived health. The questionnaire consists of 6 charts on health status and a total of 7 questions with five possible answers.

Assessed using the validated Spanish version of the GHQ-12 (General Health Questionnaire), which evaluates overall psychological well-being to detect non-psychotic psychiatric problems.The total score ranges from 0 to 12, with higher scores indicating poorer mental health. A cutoff score above 3 suggests psychological distress.

Assessed using the DUKE-UNC-11 (Duke-UNC Functional Social Support Questionnaire).The total score ranges from 11 to 55, categorizing the individual's perceived social support as "low" (below 32) or "normal" (32 or above)

To assess dynamic activation, a pelvic mobility test will be used. To assess activation, internal oblique, lumbar multifidus, gluteus maximus, and tensor fasciae lataewill be recorded simultaneously.

The pelvic mobility test will be the same one used to analyze biomechanical variables. It will consist of an assessment in both standing and seated positions at 45° flexion, during which the electromyographic activity of the aforementioned muscles will be recorded simultaneously. The percentage of muscle activation during anterior and posterior pelvic tilts will be calculated in both standing and seated positions.

The gait test will involve walking on a treadmill for one minute at a comfortable speed chosen by each patient. Two repetitions will be performed. Additionally, each subject will have an adaptation period to ensure they feel comfortable during the test.

The speed achieved by each participant will be recorded, as lower speeds are associated with protective mechanisms.

A maximum voluntary isometric contraction (MVIC) test will be performed for the biceps femoris, gluteus maximus, lumbar multifidus, internal oblique , and tensor fasciae latae using a wireless surface electromyography (EMG) system (Trigno Avanti, Delsys, Natick, USA).

The electrode placement will follow the SENIAM recommendations. Each test will be performed for 3 seconds with 20 secons rest. The percentage of activation and peak activation will be recorded for each test.

Height in centimeters using a stadiometer.

Fat mass wil be assessed using the Tanita bioelectrical impedance analyzer, with results expressed as a percentage relative to total body mass.

waist circumference using a non-extensible plastic tape (TECSYMP Instruments: 0-2 m).

Muscle mass wil be assessed using the Tanita bioelectrical impedance analyzer, with results expressed as a percentage relative to total body mass.