Fascia thickness of individuals with chronic low back pain will be measured by ultrasound and the relationship with pain, flexibility, disability and depression will be analysed.

To investigate the thickness of the fascia tissue, the subjects will undergo an ultrasound examination using a clinical ultrasound system (S9, SonoScape Corporation, made in China) with a linear 5-14 MHz array of L14-5/38. The transducer with a cross-section of 6.24 cm2 will be aimed at points 2 cm lateral to the midline of the L2 and L3 vertebrae on both sides of the spine.

The Visual Analog Scale, a 100 mm long scale marked at every 10 mm and ranging from 0 to 10, will be used to assess the level of pain. Patients mark their own pain level on this scale, scoring between 0 and 10, where 0 indicates "no pain" and 10 represents "the worst possible pain"

The Straight Leg Raise Test is a physiotherapy method used to determine the range of motion of the hip joint. The patient lies supine. They are instructed to lift one leg as high as possible without bending the knee. The leg that remains on the ground should not lift, and its knee should remain extended. The point reached by the raised leg is measured with a goniometer. The same procedure is repeated for the other leg . Normally, the hip flexion angle is 90 degrees; a range of 70-90 degrees is considered normal in adults. An angle below 70 degrees indicates restriction.

This physiotherapy method is used to evaluate the shortening of the extensor muscles in the lumbar region. The patient lies supine with their arms in a reverse 'T' position. They are instructed to flex both hips and knees and draw them towards their abdomen. The distance between the knees and the chest is recorded

The Turkish version of the Roland Morris Disability Questionnaire will be used to measure disability. The RMDQ, first published in 1983, assesses the disability level of individuals with back pain(23). It consists of 24 items, including physical ability/activity (15 items), sleep/rest (3 items), psychosocial (2 items), home management (2 items), eating (1 item), and pain frequency (1 item). The original 24-item questionnaire has been shortened to 18-item and 23-item versions and adapted for use in other countries . It was adapted into Turkish by Küçükdeveci et al. in 2001. Each positive response corresponds to one point on the scale, addressing daily activities potentially restricted by back pain. Each "Yes" answer scores 1 point, and each "No" answer scores 0 points, with the final score being the sum of these points. The total score ranges from 0 to 24, with higher scores indicating greater disability .