PURPOSE: this study aimed to investigate the effect of opposite knee position on hamstring flexibility BACKGROUND Hamstrings tightness is one of the most common findings in patients with LBP. It is thought that, due to the attachments of hamstrings to the ischial tuberosity, hamstrings tightness generates posterior pelvic tilt and decreases lumbar lordosis, which can result in LBP.

HYPOTHESES There will be significant difference in the hamstring flexibility with changing position of opposite knee (flexed or extended) in patients with mechanical low back pain.

RESEARCH QUESTION: Will changing position of opposite knee (flexed or extended) affect the hamstring flexibility in patients with mechanical low back pain?

• The subject will be instructed to maintain 90° hip flexion in the supine position.
• Then asked to actively extend the knee joint.
• The degree of achieving active knee extension will be measured using a universal goniometer.
• The average of three active knee extension measurements will be recorded used as the hamstring muscle length for the data analysis (Dong-Kyu Lee, et al., 2018).
• This test will be done for the same limb with opposite leg extended and with opposite flexed.

Inclusion Criteria:

• Patients with history of back pain and assessed with Mechanical inflammatory low back pain index and have very high grade for mechanical component.
• Age ranges from 18-40 years.
• The body mass index of the subject is ≤25 kg/meter square.

Exclusion Criteria:

1. Previous trauma, fractures or surgery of the back.
2. Malignancy of the back.
3. Rheumatoid arthritis
4. Spondylolysis or spondylolithesis
5. History of lower extremity injury within 6 months prior to the study

• Male and female
• Age range from 18-40 years old
• With previous mentioned inclusion criteria