Red Light Therapy for Achilles Tendon Injury: Scientific Evidence

Researchers in Sweden evaluated high-power laser treatment against a placebo version of it for long-standing Achilles tendon pain, in a 2016 randomized controlled trial. 40 patients received 6 treatments of either the active or the placebo device across 3 to 4 weeks, using 980 nm near-infrared light delivering 520 J, and were followed for a further 8 to 12 weeks. Rated pain fell further in the active group than in the placebo group, with the difference reaching significance on 4 of the 9 questions about loading the foot and ankle, and the pressure needed to cause pain rose in the active group. According to the study, high power laser treatment may offer a future option for this pain, though results varied between individuals and further work is needed.

Placebo and active laser were each paired with 2 different exercise schedules, giving 4 groups in a 2016 randomized controlled trial of photobiomodulation for long-standing Achilles tendon pain. 80 participants aged 18 to 65 with symptoms lasting longer than 3 months were randomly assigned and assessed at the start, at 4 weeks, and at 12 weeks, with the treated groups receiving 810 and 980 nm near-infrared light at 5 and 10 W for 90 seconds, delivering 6.66 J/cm². The group receiving active laser with the lighter exercise schedule gained significantly more on the main tendon questionnaire at 12 weeks than each of the other 3 groups. 16 participants were lost to follow-up by 12 weeks, 4 of them because of adverse reactions. Twice-weekly exercise appeared to match twice-daily exercise, with photobiomodulation adding further benefit on top.

Complete skin closure was reached in 10 of 13 patients with deep, long-standing wounds over the Achilles tendon, in a 2011 observational study at a wound care center in Israel. Of 80 patients seen, 15 were referred for amputation, and 52 were treated elsewhere, leaving 13 who could attend 2 to 3 times per week and received topical oxygen followed by low-level laser therapy (LLLT) and moisture-retaining dressings, using 560, 632.8, and 785 nm light at 6 to 80 mW and 0.9 to 0.95 J/cm². Patients had a median age of 73 years, among whom most had diabetes, and wounds averaged 90 cm². Healing took a mean of 19 weeks, and 7 of the 10 who healed were still walking and free of ulcers at a mean follow-up of 3.3 years. The study found the outcomes encouraging given the severity of these wounds, while calling for research to clarify what each part of the protocol contributes.

In a 2009 observational study, 8 healthy men pushed the ball of their foot down against resistance, sustaining each effort briefly or for longer. Blood volume and oxygen levels in the Achilles tendon and the calf muscle were measured using red and near-infrared light at 635, 650, 690, 780, 810, and 830 nm shone through the skin, with the light used only to take readings rather than as a treatment, and tendon stretch recorded at the same time. Blood volume and oxygen levels in the tendon rose after the brief efforts but not after the longer ones, while the tendon became more flexible after the longer efforts but not the brief ones. The duration of the effort appeared to affect not only tendon flexibility but also its blood supply.

Comparing lengthening exercises plus low-level laser therapy (LLLT) against lengthening exercises plus a placebo laser, a 2008 randomized controlled trial followed recreational athletes with long-standing Achilles tendon pain. 52 athletes were randomly assigned in a blinded manner across 8 weeks, with the treated group receiving 820 nm near-infrared light at 60 mW/cm² to 6 points along the tendon across 12 sessions, giving 5.4 J per session. Pain during activity, rated on a 100-mm scale, was 53.6 vs 71.5 at 4 weeks, 37.3 vs 62.8 at 8 weeks, and 33.0 vs 53.0 at 12 weeks, favoring the laser group each time. According to the trial, morning stiffness, ankle movement, tenderness on pressing, and joint creaking all followed the same pattern, and the laser group's results at 4 weeks matched the placebo group's at 12.

Among 12 healthy men pushing the ball of the foot down against resistance, a 2008 observational study measured blood volume and oxygen levels in the Achilles tendon. Red and near-infrared light at 635, 650, 690, 780, 810 and 830 nm was shone through the skin over the tendon and the calf muscle to take the readings, while each man first made a single sustained effort at 10, 30, 50 and 70% of his maximum, then 50 short repetitions of 5 seconds each across 10 minutes. Blood volume and oxygen levels in the tendon fell during every sustained effort, whatever the force, then rose gradually after the 50 short repetitions and stayed raised to the end of the recovery period. That rise may be linked to tendon repair after exercise that loads the tendon.

14 tendons in 7 patients with an inflamed Achilles tendon on both sides took part in a 2006 randomized controlled trial of low-level laser therapy (LLLT). Symptoms were brought on by activity immediately before the study, and both tendons of each patient were treated in random, blinded order: one with 904 nm near-infrared light delivering 5.4 J per point at 20 mW/cm², and the other with a placebo delivering no energy. A chemical marker of inflammation inside the tendon fell significantly at 75, 90, and 105 minutes after the active treatment, both compared with its baseline level and with the placebo. The pressure needed to cause pain also rose significantly after the active treatment, by 0.40 kg/cm² more than after placebo. The study concluded that LLLT at this dose can reduce inflammation and pain in an actively inflamed Achilles tendon.

Across the full range of treatments offered for long-standing Achilles tendon pain, a 2012 review assessed which options the evidence supports. The review covered lengthening exercises, shockwave treatment, a topical heart medicine applied to the skin, low-level laser therapy, supports and splints, several kinds of injection, and surgery, in patients whose symptoms had lasted more than 6 weeks. Lengthening exercises emerged as the first-line treatment for sport-related cases, while the evidence for every other non-surgical option, laser included, was judged insufficient to recommend. The review concluded that many treatments for this condition have limited evidence of benefit, and that surgery may be considered only where non-surgical care fails.

A pilot design tested whether a full trial would be feasible before judging effectiveness, in a 2008 randomized controlled trial of low-level laser therapy (LLLT) for long-standing Achilles tendon pain. 20 patients were randomly assigned to active or placebo laser, with patients, therapists, and investigators all unaware of the allocation. Everyone followed a 12-week program of lengthening exercises while receiving 810 nm near-infrared light at 100 mW to 6 points on the tendon for 30 seconds each, giving 3 J per point and 18 J per session, 3 times per week for 28 days. Both groups improved significantly on every measure at 4 and 12 weeks, apart from muscle strength in the placebo group at 4 weeks. The trial found that no judgment on effectiveness could be made because it was too small, and estimated that 20 patients per group would be needed.

46 runners with Achilles tendon pain lasting more than 3 months were randomly assigned to exercise alone, exercise plus shockwave treatment, or exercise plus shockwave plus photobiomodulation therapy (PBMT) in a 2025 randomized controlled trial. The group (40 years of age, 24 men and 22 women) was given shockwave once weekly for 3 treatments, and those assigned light also received 810 and 980 nm near-infrared light at 25 W twice a week for 3 weeks, with outcomes collected at intervals across 3 months. Exercise plus shockwave gained 33 points on the main tendon questionnaire against 18 for exercise alone, a significant difference, while adding light brought 25 points against 18, which was not significant. All 3 groups reached clinical improvement, so the trial pointed to the exercise program as the common factor.

When researchers paired lengthening exercises with either an active or a placebo laser, a 2024 randomized controlled trial tested whether the light added anything for pain in the middle of the Achilles tendon. 60 patients aged 18 to 60 were randomly split into 2 groups of 30, averaging 33.9 and 33.4 years of age, with the treated group receiving 820 nm near-infrared light at 66.67 mW, delivering 8 J for 2 minutes across 56 days. Both groups improved significantly over time on the tendon questionnaire and on pain, but no significant difference appeared between them at any point. The study concluded that lengthening exercises should stay the main treatment and that light should be considered only as an addition.

A 2022 randomized controlled trial investigated photobiomodulation added to non-surgical treatment of a ruptured Achilles tendon. 34 men with a recent rupture on 1 side, averaging 45.5 and 48.7 years of age across the 2 groups, were split evenly between photobiomodulation and a sham. All went through a period in a cast followed by rehabilitation sessions twice a week for 12 weeks covering strengthening, movement range, and balance, with the treated group receiving a cluster of 904, 858, and 658 nm light. Both groups improved in rupture score, movement range, calf strength, and pain. The trial found no significant differences between the groups on any outcome.

According to a 2020 meta-analysis of 4 randomized controlled trials covering 119 participants, the case for low-level laser therapy in long-standing Achilles tendon pain does not hold up. The review searched 10 databases through February 2020 for trials comparing laser therapy with inactive or active treatments, and the pooled trials used 810, 820, and 830 nm light across a wide range of settings. Laser added to lengthening exercises showed very low to low certainty of evidence for both pain and function. Although 1 trial favored laser at 2 months, the confidence intervals at 3 and 13 months included no important difference, while function at 1 month favored the placebo group. The review found the evidence insufficient to support routine use of laser therapy for this condition.

This 2019 clinical trial looked at whether photobiomodulation (PBM) changes the structure or mechanical behavior of the Achilles tendon within 4 hours. 20 people with healthy tendons and 12 with long-standing Achilles tendon pain each had 1 tendon treated and the tendon on the other side given a placebo, with 810 and 980 nm near-infrared light at 5 and 10 W applied for 90 seconds to deliver 6.66 J/cm², and both sides assessed before treatment, straight after, and at 2 and 4 hours. No immediate difference appeared between the treated and placebo sides in either group, and the effect did not differ between healthy and injured tendons. The study concluded that PBM can therefore be given before other treatments or before heavy activity.

No difference in the main outcome appeared between laser and placebo in a 2012 randomized controlled trial of low-level laser therapy (LLLT) added to lengthening exercises. 40 patients with pain in the middle of the Achilles tendon were randomly assigned to 2 groups averaging 45.6 and 46.5 years of age, all performing lengthening exercises across 3 months and receiving active or placebo light 3 times per week for the first 4 weeks at 810 nm and 3 J per point, with 36 completing the 12-week assessment and 33 the 52-week assessment. Scores on the main tendon questionnaire showed no significant difference between the groups at any point, and at 4 weeks the difference significantly favored the placebo group. The trial found that adding LLLT to lengthening exercises had not been shown to work in these settings.