The study will establish data on the function of trunk muscles in healthy and low back pain patient's pre and post dry needling treatment. This will help in understanding the underlying mechanism of this treatment and reveal the effect of dry needling on muscle performance.

Study hypothesis is that an improvement of back muscle function following dry needling procedure will be found.

Dry needling of muscles is mainly used for the management of pain in musculoskeletal disorders. Yet, the association between dry needling and motor performance of muscles is still unclear.

This study aims to investigate the immediate effect of dry needling on lumbar multifidus muscles' function in healthy and low back pain subjects.

The sample will be divided into: low back pain group and control (healthy) group. Both groups will receive dry needling to the lumbar multifidus muscles using a deep insertion technique with 4 needles (2 on each side of the spine). The needles will be left in situ for 10 minutes. Ultrasound imaging will be used to measure multifidus muscles' thickness, pre and post- procedure during rest in a prone position and during contralateral active straight leg extension.

Inclusion Criteria:

• Age: 18-60 years.
• Healthy individuals or individuals with main complaint of low back pain (LBP)

Exclusion Criteria:

• Patients with "red flags" for a serious spinal condition, for example: tumor, compression fractures, infection, cancer.
• Signs of nerve root compression (positive straight leg raise <45 degrees, decreased reflexes, decrease sensation or decreased strength in the lower extremities).
• Pregnancy.
• Previous surgery to the lumbar spine
• History of congenital lumbar or pelvic anomalies
• Physical therapy for LBP was provided in the 6 months prior to participation in the study
• Patients who are unable to lie prone for 30 minutes.