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The Healing Power of Light: Low-Level Laser Therapy in Tendon Repair .

If physiotherapy was a person, he would be a mastermind magician with thousands of tricks up his sleeve. The profession is extremely intricate and there is slight chance clinicians may get their treatment options tangled up. One such card every therapist has up their sleeve is electrotherapeutic modalities. One such modality that has been clinically proven to be effective is low-level laser therapy. 

Low-level laser therapy is a form of laser medicine used in physical therapy, which uses low-level lasers or light-emitting diodes to alter cellular functions. Low-level laser therapy has various other names like low-power laser, soft tissue lasers, cold lasers, biostimulation laser, therapeutic laser, and laser acupuncture. The term Laser is the acronym for Light Amplification by Stimulated Emission of Radiation.  Low-level laser therapy is used by some physiotherapists to treat various musculoskeletal conditions. It is a non-invasive light source treatment that generates a single wavelength of light. It emits no heat, sound, or vibration. It is also called photobiology or biostimulation. It is also believed to affect the function of connective tissue cells, accelerate connective tissue repair and act as an anti-inflammatory agent. 

A laser device generates light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. Light with a wavelength in the red to near infrared region of the spectrum (660nm–905nm), is generally employed because these wavelengths have the ability to penetrate skin, and soft/hard tissues and are proven in clinical trials to have a good effect on pain, inflammation and tissue repair. The power density (irradiance) is usually between 5W/cm2 and is applied to an injury or to a painful site for 30–60 seconds a few times a week for several weeks. The result is a reduction of inflammation, pain relief and accelerated tissue regeneration. 

The mechanism of action of LLLT is based on the concept of photobiomodulation, which is the process of using light to stimulate and modulate cellular activity. LLLT devices emit specific wavelengths of light that are absorbed by the mitochondria within the cells of the targeted tissue. When the light is absorbed by the mitochondria, it triggers a complex cascade of biochemical reactions that lead to the production of adenosine triphosphate (ATP), the main source of energy for cells. In addition to ATP production, LLLT also stimulates the release of nitric oxide (NO), a molecule that plays a critical role in vascular function. NO is a potent vasodilator, which means that it helps to relax the smooth muscle cells in blood vessel walls, leading to increased blood flow to the treated area. This increased blood flow brings oxygen and nutrients to the damaged tissue, which helps to accelerate the healing process.

LLLT also stimulates the release of other molecules, such as cytokines, growth factors, and reactive oxygen species (ROS), which play important roles in tissue repair and regeneration. These molecules help to promote the proliferation of new cells, the formation of new blood vessels, and the regeneration of damaged tissue. 

LLLT has shown that it may reduce pain associated with inflammation by lowering the levels of prostaglandin E2 , interleukin-1 beta, tumor necrosis factor-alpha, cellular influx of neutrophils and granulocytes, oxidative stress, edema, and bleeding in a dose-dependent manner.

Since laser has shown to reduce inflammation, it means that it has the capability to provide analgesia to individuals suffering from tendinopathies, sprains, strains, and even frozen shoulder. According to the more than 4000 studies on, it can be concluded that the majority of laboratory and clinical studies have demonstrated that LLLT has a positive effect on acute and chronic musculoskeletal pain. LLLT has a long history and strong basic science evidence, which supports its use in pain management. It has few side effects and is well tolerated by the elderly. 


Now, for the real sauce, how specifically does low-level laser therapy facilitate tendon healing after an injury? 

In order to thoroughly understand, we need to learn about the three phases of tendon repair/healing. 

  1. Inflammatory phase – During the inflammatory phase, vascular permeability increases and an influx of inflammatory cells enter the healing site. These cells produce a number of cytokines and growth factors that lead to recruitment and proliferation of macrophages and resident tendon fibroblasts. This phase begins within 48 hours of the injury and lasts up to a span of a few days.
  2. Proliferation phase – The proliferative phase is mainly characterized by the formation of large amounts of granulation tissue, including the proliferation of fibroblasts and the synthesis of type III collagen. This stage lasts from the secod day up to around a couple of weeks.
  3. Remodeling phase – In the third and final stage, known as the remodeling phase, collagen I synthesis begins to dominate, and the extracellular matrix becomes more aligned. In addition, cell density and general synthetic activity are gradually decreased. This phase begins 1–2 months after injury and can last more than a year. The repaired tissue appears scar-like and never completely regains the biomechanical properties it had prior to injury.


What if I tell you that LLLT deals with each phase in a unique way? 


During the first phase, LLLT helps with angiogenesis, the formation of new blood vessels. To promote angiogenesis, LLLT works in two main ways. Firstly, it requires a low-oxygen environment, known as hypoxia, which is necessary for the formation of new blood vessels. Secondly, LLLT can regulate the activity of angiogenic factors like VEGF and matrix metallopeptidase 2 (MMP-2), which are important for tissue repair. By regulating these factors, LLLT can help to promote the growth of new blood vessels in the injured tissue.

Hypoxia-inducible factor 1α (HIF-1α) is a key factor in the process of angiogenesis in low-oxygen conditions. When tissue is exposed to LLLT, the absorption of photons is accompanied by an increase in the respiration rate, which leads to a drop in the amount of oxygen in the tissue. This drop in oxygen levels can activate HIF-1α, which in turn promotes the growth of new blood vessels in the injured tissue.

LLLT works by stimulating the tissue with light, not heat. HIF-1α is important in promoting angiogenesis in low oxygen conditions, which is necessary for LLLT to work. LLLT can also regulate angiogenic factors like VEGF and MMP-2, which are important for tissue repair.


During the second stage, low-level laser therapy helps tendons heal better by promoting the growth of fibroblasts, which are cells that produce collagen, an important component of tendon tissue. Fibroblast activity is mainly influenced by a growth factor called transforming growth factor-β (TGF-β), which is essential for tendon repair and reducing the number of senescent cells, cells that can contribute to tissue degeneration.

TGF-β has two main functions – promoting wound healing and scar formation, and playing a key role in muscle fibrosis. LLLT can reduce the amount of TGF-β in the injured tendon tissue, which can reduce the likelihood of complications like tendon tearing after surgery, and indirectly promote collagen synthesis. By regulating TGF-β, LLLT can help to promote the growth of healthy tendon tissue and prevent fibrosis.


For the third stage, LLLT reduces inflammatory response during the tendon shaping. LLLT can decrease the expression of the NF-kB gene, reduce the activity of COX-2, lower the number of inflammatory mediators and pro-inflammatory factors, and activate M2 macrophages to release anti-inflammatory factors, thus producing anti-inflammatory effects and promoting tendon repair 


Tendon injury is a series of muscular imbalances caused by muscle overstrain or poor treatment at the beginning of the disease. Overloading can lead to partial tearing of the tendon initially, and tendon tears are often accompanied by some inflammation and degeneration of the tendon. If not treated in a timely fashion, it will cause structural imbalance and tendon tears, and other consequences.

In conclusion, low-level laser therapy is a safe, non-invasive, and effective treatment option for a variety of musculoskeletal conditions. It works by stimulating the body’s natural healing processes, promoting tissue repair, reducing pain and inflammation, and increasing blood flow to the treated area. The evidence supporting the use of LLLT is strong, and it has been shown to be effective in clinical trials and studies. However, while LLLT can be a powerful tool in treating musculoskeletal conditions, it should not be used as the only method of treatment. Other treatments, such as physical therapy, medications, and lifestyle changes, may be necessary to achieve optimal results. It is also important to be realistic about the potential benefits of LLLT, as it may not work for everyone and may not provide immediate relief.

Overall, LLLT is a valuable treatment option for those suffering from musculoskeletal conditions, but it should be used as part of a comprehensive treatment plan and under the guidance of a qualified healthcare professional.


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