Red light therapy — more precisely called photobiomodulation — has genuine biological plausibility for supporting tendon repair. The mechanisms are real, the animal evidence is interesting, and clinicians use it in practice. But the only double-blind randomised controlled trial conducted specifically on Achilles tendon rupture patients found it was not superior to conservative treatment alone. Here is what the evidence actually shows — and what to make of it.
In this article
Red light therapy panels are increasingly common — in physiotherapy clinics, in gyms, in elite sports facilities, and in people's homes. The marketing around them is often extravagant. After an Achilles rupture, when you are looking for anything that might accelerate healing, the proposition is appealing: shine some light on the tendon, improve circulation and collagen synthesis, heal faster.
The honest answer is more complicated than that. The biological mechanisms are plausible and reasonably well understood. Animal studies are promising. But the human evidence for Achilles tendon rupture specifically is thin — and the most rigorous study available found no benefit over doing nothing with light at all.
This article covers what photobiomodulation is, what the proposed mechanisms are, what the evidence actually shows at each level, and how to think about whether it is worth pursuing.
- What Is Photobiomodulation?
- The Proposed Mechanisms
- The Animal Evidence
- The Human Evidence
- How to Read the Evidence
- Practical Considerations
What Is Photobiomodulation?
Photobiomodulation (PBM) is the use of red and near-infrared light to influence biological processes in tissue. It is also called low-level laser therapy (LLLT) or low-level light therapy. The terms are used interchangeably in the research literature, though there is a technical distinction: LLLT traditionally refers to laser-based delivery, while PBM encompasses both lasers and LED-based devices.
The light used is in the red (approximately 630–700 nm) and near-infrared (approximately 700–1100 nm) wavelength range. It is non-ionising — it does not damage tissue the way UV radiation or X-rays do. It emits no meaningful heat at clinical doses. The proposed mechanism of action operates at the cellular level rather than through thermal effects.
Terminology
Photobiomodulation (PBM) is the current preferred scientific term. Low-level laser therapy (LLLT) is the older term, still widely used in published research. Red light therapy is the consumer term. Near-infrared therapy refers to the longer-wavelength end of the spectrum. All refer to the same general category of treatment. The 2024 JOSPT Clinical Practice Guidelines use "low-level laser therapy" for this modality, defined as a single wavelength light source between 632 and 904 nm with output power below 0.5 W.
The Proposed Mechanisms
The biological rationale for PBM in tendon healing is reasonably well established at the cellular level. The primary proposed mechanism involves photon absorption by cytochrome c oxidase — a key enzyme in the mitochondrial electron transport chain. Light absorption by this enzyme is thought to increase mitochondrial activity and ATP production, which in turn increases cellular energy availability for repair processes.
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Primary cellular mechanism
Photon absorption by cytochrome c oxidase increases mitochondrial ATP production
Cytochrome c oxidase, located in the inner mitochondrial membrane, absorbs photons in the red and near-infrared range. This absorption is proposed to partially reverse the inhibition of cytochrome c oxidase by nitric oxide, increasing electron transport and ATP synthesis. The increased ATP availability supports fibroblast activity — the cells responsible for producing collagen in tendon tissue. This mechanism is the most studied and best supported in the PBM literature, though it remains an area of active research.
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Collagen synthesis
PBM stimulates fibroblast proliferation and collagen production in tendon tissue
Multiple in vitro and animal studies have demonstrated increased fibroblast proliferation and collagen synthesis following PBM exposure. A 2021 rat study (PubMed 33755188) found that PBM at 780 nm stimulated mesenchymal cell proliferation and significantly increased collagen type II gene expression in partially sectioned Achilles tendons. A 2025 murine model study (Lim et al., Int J Mol Sci) using LED irradiation at 630 nm and 880 nm found improved tendon healing histologically, with inhibition of excessive cell density and nuclear circularity — markers of scar tissue formation. These are animal findings, not human clinical outcomes.
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Microcirculation
Near-infrared PBM increases microcirculatory blood flow in treated tissue
The Achilles tendon is a poorly vascularised structure — its limited blood supply is one reason tendon injuries heal slowly. Research by Gavish et al. demonstrated that near-infrared PBM significantly increases microcirculatory blood flow in treated areas. Improved local circulation would theoretically support the delivery of nutrients and growth factors to healing tendon tissue. This mechanism is plausible and clinically relevant given the tendon's vascularity challenges, but the clinical translation to improved rupture outcomes remains unproven.
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Inflammation modulation
PBM may modulate the inflammatory response during early healing
PBM is proposed to reduce excessive inflammation while preserving the beneficial acute inflammatory response needed for healing. This biphasic effect — reducing chronic or excessive inflammation without eliminating acute inflammation — is theoretically well-suited to tendon rupture recovery, where the early inflammatory phase is necessary for healing but prolonged inflammation impedes remodelling. The evidence for this mechanism in human Achilles rupture is limited.
The Animal Evidence
Animal studies — primarily rat and murine models of Achilles tendon injury — consistently show positive effects of PBM on tendon healing markers. These include increased collagen synthesis, improved fibre alignment, reduced scar tissue formation, and better histological appearance of healing tissue.
The 2025 Lim et al. study (International Journal of Molecular Sciences) created a murine Achilles tendon rupture model and applied combined LED irradiation at 630 nm and 880 nm for 20 minutes. Histological analysis showed PBM therapy improved tendon healing through inhibition of excessive cell density and nuclear circularity — characteristics associated with fibrotic scar formation rather than functional tendon tissue.
A 2021 rat study published in PubMed (33755188) found significantly higher collagen type II gene expression in PBM-treated tendons versus controls after partial section injury, alongside increased mesenchymal cell proliferation in the injury region.
The standard caveat applies fully here: animal models of tendon injury differ from human Achilles rupture in important ways — the injury mechanism, the healing biology, the loading environment, and the scale. Findings in rat tendons do not reliably predict clinical outcomes in humans.
The Human Evidence
This is where the picture becomes considerably more complicated — and where intellectual honesty requires setting aside the optimistic animal findings and asking what the clinical evidence actually shows.
Achilles tendinopathy (not rupture)
The human evidence base for PBM in Achilles conditions is primarily built on tendinopathy studies — chronic overuse injury, not acute rupture. A 2008 clinical trial by Stergioulas et al. (American Journal of Sports Medicine) found that adding low-level laser to an eccentric exercise program produced better pain and function outcomes at 12 weeks than eccentric exercise with sham laser. This is one of the better-designed tendinopathy trials and is frequently cited in support of PBM for Achilles conditions.
However, a 2020 systematic review examining multiple trials in Achilles tendinopathy patients concluded that the results were inconsistent and the overall evidence quality was low. The 2024 Clinical Practice Guidelines from the Academy of Orthopaedic Physical Therapy (JOSPT, 2024) — arguably the most authoritative clinical reference document on Achilles tendinopathy — concluded that low-level laser therapies showed no significant effects on function or pain in individuals with midportion Achilles tendinopathy.
Tendinopathy ≠ Rupture
Achilles tendinopathy is chronic degenerative overuse injury. Achilles tendon rupture is acute structural failure. The healing biology, the clinical presentation, the rehabilitation protocol, and the relevant outcomes are all different. Evidence from tendinopathy studies does not transfer directly to rupture recovery.
The key RCT — Achilles tendon rupture specifically
The most important piece of evidence for anyone considering PBM after an Achilles rupture is a 2022 double-blind, superiority, randomised controlled trial published in Archives of Rehabilitation Research and Clinical Translation (de Oliveira et al., PMID 36545533).
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de Oliveira et al., 2022 — The pivotal RCT
Photobiomodulation was not superior to conservative treatment alone for improving function in acute Achilles tendon rupture
This prospective, patient- and assessor-blinded, parallel RCT enrolled 34 male patients with acute unilateral Achilles tendon rupture treated conservatively — divided equally into a photobiomodulation group and a sham group. Both groups received identical conservative treatment protocols. The PBM group received red and near-infrared light treatments applied at three sites on the injured Achilles (proximal, mid-portion, and distal near the calcaneus insertion) during the immobilisation period while in the boot. The sham group received identical treatment positioning with inactive devices. Both groups then completed the same rehabilitation protocol. The primary outcome was the Achilles Tendon Rupture Score (ATRS). Conclusion: photobiomodulation associated with conservative treatment is not superior to conservative treatment alone for improving function in patients with acute ATR.
This is a well-designed trial — blinded, controlled, specific to the injury in question. It is the most direct evidence available on whether PBM adds meaningful benefit to standard Achilles rupture management. The result was null: no significant advantage for the PBM group.
It is a small trial (n=34) and was conducted only in conservatively managed patients. It does not address whether PBM might benefit surgically repaired ruptures, or whether different dosing protocols might produce different results. These are genuine limitations. But it is the most rigorous evidence available, and it found no benefit.
How to Read the Evidence
There is a pattern in emerging therapies that is worth understanding. A plausible mechanism is identified. Animal studies confirm the mechanism operates in tissue. Early, smaller human studies show promising results. Larger, better-controlled studies then frequently fail to replicate those results.
PBM for Achilles conditions follows this pattern closely. The mechanism is plausible. The animal findings are consistently positive. The human evidence is inconsistent, and the best-designed trial for the specific injury is null.
This does not mean PBM definitively does not work. The 2022 RCT was small, the dosing protocol may not have been optimal, and the follow-up period may have been insufficient to detect differences in tendon remodelling quality. Further research may produce different conclusions. But the current evidence does not support adding PBM to standard Achilles rupture rehabilitation on the basis of expected functional benefit.
"The most rigorous trial available found no benefit. That does not prove it does not work — but it means the burden of proof has not been met."
Practical Considerations
If you are considering red light therapy during Achilles rupture recovery, the evidence picture should inform your decision — not paralyse it. A few practical points:
- The risk profile is very low. PBM at clinical doses has no established harmful effects on healing tissue. If you already have access to a device and the cost is not a burden, using it is unlikely to cause harm.
- It is not a replacement for rehabilitation. The evidence base for structured rehabilitation — progressive loading, physiotherapy-guided return to activity — is far stronger than for any adjunct therapy. If using PBM comes at the expense of attention to the fundamentals, the trade-off is negative.
- Device quality and dosing matter. Consumer-grade red light panels vary significantly in wavelength accuracy, power output, and treatment area. The clinical studies use precisely calibrated devices. Whether a home device delivers equivalent dosing is genuinely uncertain.
- Wavelength matters. Studies have used wavelengths between 630 nm and 904 nm. Near-infrared wavelengths (800–900 nm) penetrate deeper into tissue and may be more relevant for a structure like the Achilles that sits below the skin. Red wavelengths (630–700 nm) penetrate less deeply.
- The Achilles is deeper than it appears. The tendon sits several centimetres below the skin surface. Light intensity diminishes significantly with tissue depth. Whether meaningful photon delivery reaches the tendon from an external device is a genuine question.
The Bottom Line
The biological mechanisms are plausible, animal evidence is promising, and PBM appears safe. But the only double-blind RCT on Achilles tendon rupture specifically found no functional benefit over conservative treatment alone. PBM may be a reasonable low-risk adjunct for those who want to explore it, but it should not displace or distract from evidence-based rehabilitation. Discuss it with your physiotherapist before incorporating it into your recovery.
References
1. de Oliveira PR, Arrebola LS, Stéfani KC, Pinfildi CE. Photobiomodulation associated with conservative treatment for Achilles tendon rupture: a double-blind, superiority, randomized controlled trial. Arch Rehabil Res Clin Transl. 2022;4(4):100219.
PubMed 365455332. Lim JK, Kim JH, Park GT, et al. Efficacy of light-emitting diode-mediated photobiomodulation in tendon healing in a murine model. Int J Mol Sci. 2025;26(5):2286.
MDPI3. Photobiomodulation therapy increases collagen II after tendon experimental injury. PubMed. 2021. PMID 33755188. Rat model, 780 nm PBM, increased COLA2 expression and mesenchymal cell proliferation.
4. Stergioulas A, Stergioula M, Aarskog R, Lopes-Martins RA, Bjordal JM. Effects of low-level laser therapy and eccentric exercises in the treatment of recreational athletes with chronic Achilles tendinopathy. Am J Sports Med. 2008;36(5):881-887.
5. Achilles Pain, Stiffness, and Muscle Power Deficits: Midportion Achilles Tendinopathy Revision — 2024 Clinical Practice Guidelines. Journal of Orthopaedic and Sports Physical Therapy. 2024;54(12). Conclusion: low-level laser therapies showed no significant effects on function or pain in midportion Achilles tendinopathy.
JOSPT6. Atik OS. Photobiomodulation for Achilles tendinopathy. Photobiomodul Photomed Laser Surg. 2018. Fibroblast proliferation, collagen synthesis, and tensile strength — preclinical mechanisms.
7. Lawrence J et al. Photobiomodulation as Medicine: Low-Level Laser Therapy (LLLT) for Acute Tissue Injury or Sport Performance Recovery. J Funct Morphol Kinesiol. 2024;9(4):181.
PubMed 394494758. Treat My Achilles. Red light therapy for Achilles tendonitis and tears — benefits and drawbacks. November 2025. Clinical summary and evidence overview. treatmyachilles.com
General health information only. This article is not medical advice. Decisions about adjunct therapies during Achilles tendon rupture recovery should be made in consultation with your physiotherapist or treating clinician.
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