Chronic low back pain (CLBP) is a major public health concern worldwide, leading to reduced quality of life and significant work loss. It is defined as pain lasting more than 12 weeks between the lumbar and sacral spinal segments. The global prevalence of CLBP ranges from 13.1% to 20.3%, and the number of affected individuals has increased from 370 million in 1990 to 570 million in 2017.

Core muscles, including the multifidus, erector spinae, transversus abdominis, psoas major, and quadratus lumborum, play a key role in spinal stabilization. In patients with CLBP, dysfunction and loss of synergy among these muscles can compromise spinal balance. Prolonged poor posture can reduce the strength and endurance of the lumbar erector spinae, multifidus, and transversus abdominis, leading patients to compensate by overusing the erector spinae, rectus abdominis, and oblique abdominal muscles. This compensation is considered one of the primary contributors to chronic low back pain.

These deep core muscles can be objectively evaluated using ultrasonography (USG), a non-invasive, inexpensive, and accessible imaging method. Strain elastography, a quantitative ultrasonographic technique, is increasingly used to assess tissue stiffness and monitor structural changes in muscle over time.

Conventional treatments for CLBP include pharmacotherapy, exercise, and physical therapy. In recent years, extracorporeal shock wave therapy (ESWT) has emerged as a non-invasive, easily applicable, and low-risk treatment method. ESWT is widely used in various musculoskeletal conditions such as lateral epicondylitis, patellar tendinopathy, and calcific tendinitis of the shoulder. Studies have shown that ESWT provides pain relief and functional improvement in patients with CLBP through its angiogenic, anti-inflammatory, analgesic, and tissue-regenerative effects.

Several studies have demonstrated the positive impact of ESWT on pain reduction and functional recovery in CLBP. A recent meta-analysis reported that ESWT significantly reduces pain in CLBP patients and may be superior to other conservative treatments. Yue et al. (2021) highlighted the short-term benefits of ESWT in reducing pain and disability, while also emphasizing the need for well-designed randomized controlled trials (RCTs) to establish high-quality evidence. Similarly, Wu et al. (2023) underscored the necessity of including objective outcomes in future RCTs to better evaluate the efficacy of ESWT.

Although numerous studies have assessed the effects of ESWT on pain, disability, and functional outcomes in CLBP, to date, no study has objectively evaluated its effectiveness using ultrasonographic strain elastography focusing on the elasticity and stiffness of core muscles.

This study aims to be one of the first to assess the long-term effects of ESWT using objective measures. Its contribution to the literature lies in evaluating the efficacy of ESWT, when added to conventional physical therapy, through long-term monitoring with ultrasonographic strain elastography in patients with CLBP.

Inclusion Criteria:

• Age ≥ 18 years
• Non-specific low back pain lasting more than three months

Exclusion Criteria:

• Specific lumbar spine diseases (radicular pain, spinal stenosis, infection)
• History of trauma, fracture, surgery, or presence of scar tissue in the lumbar region
• Presence of a disease that may affect muscle stiffness, such as collagen tissue disorders, hemiplegia, multiple sclerosis, or myopathies
• Malignancy, pregnancy, severe hypertension
• Coagulopathy, chronic heart disease
• Ankylosing spondylitis
• Diseases that may initially affect lumbar mobility and pain, such as leg length discrepancy, hip prosthesis, or scoliosis