This study is designed as a pre and post experimental study. The purposes of this study are to evaluate the effect of core muscles training in patients with chronic mechanical low back pain according to SALIBA'S postural classification system (SPCS) in terms of pain intensity, function, and core muscles endurance.

Male and female patients diagnosed with chronic mechanical low back pain will be referred to physical therapy department. Patients will then be screened based on the inclusion and exclusion criteria of the current study. They will be asked to sign the informed consent form. Then, participants will be assessed for the severity of pain, functional disability, and core endurance test at baseline and at the end of the treatment by the same physiotherapist.

In addition, participants will be instructed to stand in habitual posture while looking forward and will be photographed from sagittal plane wearing shorts(males) and a thin clothes(female). The photos will be used to subjectively classify the patients into one of the 6 postural classification groups (G1, G2, G3,G4, G5, G6). The Vertical compression test and elbow flexion test will be used to objectively confirm the classification.

Later, photos will be then entered by researcher to Kinovea software for more objective confirmation of the classification.

Then, Participants will be allocated purposive randomly to one of the six groups according to evaluation criteria(saliba's postural classification system).

Then, Patients in each postural category will receive a 4-week program of core muscles training.

Two tests will be used to further confirm the classification of patients' posture.

These tests are:

1. Vertical compression test (VCT): Patient position: the patient will be asked to stand in a natural position and relax everything but the knees (so as not to buckle and collapse when pressure is applied) Therapist's position and manual contact: Standing side by side or stride position, therapist may be positioned on a stool, chair, or table. Therapist positions forearms vertical then hovers and place hands on the patient's shoulders, between the acromion and the first rib insertion. Therapist must ensure that all force is directed to patient and not allow movement in his or her body unless patient buckles. Therapist's action and verbal command: After instruction, apply gentle, sustained pressure vertically through the patient's trunk or pelvis. Gradually build the pressure from a grade of (1) which is at the point. Where the therapist feels the pressure of the patient's bony surfaces through the soft tissue covering the carpal ridge, to a (2) which is double the pressure of (1), and then to a (3) which is triplethe pressure of (1), and so on until full force is applied which would be a grade of (5). An efficient response is one in which the pressure applied by the therapist translates evenly to the base of support. In standing that would be to the arch of the foot, translating into the second ray. An efficient response is a springy end feel An inefficient response (failure) is noted when the pressure applied by the therapist causes the spine to side bend, backward bend, shear or rotate. In addition, an inefficient response is a hard end feel.

2-Elbow flexion test (EFT): Purpose: to test the proper timing of core and global muscles in response to an external load through the forearms and confirm findings of the CoreFirst Patient's position: In Standing, patient's elbows will be bent to 90 degrees, forearms supinated to loose-packed position and humerus is perpendicular to the floor, not flexed or extended and no substitution of shoulder adduction allowed to assist in stabilization. Therapist's position and manual contact: Therapist stands in front of patient, may be in squat position for resistance from below and therapist may also apply resistance from above. Therapist positions forearms perpendicular to floor then hovers. Hand placement is over the distal end of the forearm. Verbal command: "Don't let me straighten your arms". Once the command is given, the therapist gradually increases the downward resistance, being cautious NOT to pull forward while pushing or pulling down. Grading is 1-5, with "1" defined as the amount of pressure requires to feel the bones of your hands on the bones of the patient's forearms, and 2 = 2x1, 3 = 3x1, 4 = 4x1, and 5 - 5x1. When applying the resistance, the therapist asks the patient to note where the effort is and how hard it feels to maintain the position. The patient should note if the effort is in the cervical, shoulder girdle, thoracic spine, lumbar spine, or forearms. An efficient state is one in which the patient can maintain the elbow position through automatic activation of the core, rotator cuff, shoulder girdle, and global shoulder and arm muscles. The spine should remain stable, and the patient should maintain his balance. In an inefficient state, the patient will attempt to maintain the position with global muscles and will often give in the arms, shoulder girdle, and spine. The patient will frequently fall forward as the force is applied or tilt the upper body back to compensate for the load.

Inclusion Criteria:

• Patients referred with a diagnosis of CMLBP of at least 3 months.

  • Age ranging from 20 to 55 years old.
  • Both genders will be included.
  • BMI(18.5-24.9).

Exclusion Criteria:

• Lumbar canal stenosis.

  • History of vertebral fractures.
  • patients with neurological deficits such as altered sensation.
  • Spinal surgery or failed back surgery.
  • cardiovascular/ pulmonary disorder