Red Light and Muscle Soreness After a Workout: What Happens to the Muscle in the Following 72 Hours

The pain you feel today when going down the stairs isn't from today's workout. It's from the workout before yesterday. It has a name — delayed onset muscle soreness, or DOMS (from the English delayed onset muscle soreness) — and its own calendar: it appears when you've already forgotten the effort, gets worse when it's least convenient, and only disappears when it feels like it.

Curiously, in October 2026, a meta-analysis published in the journal Science & Sports looked precisely at that calendar. It didn't just ask "does red light help?", but rather "when does it help?". And the answer changes the way we can think about recovery: photobiomodulation was associated with less muscle pain up to 72 hours and more strength up to 96 hours after exercise.

In this article, we follow the muscle hour by hour, explain what red light and near-infrared do inside it, show what the studies say — including those that found no effect — and explain how to use a panel at home in a sensible way.

The 72-hour clock: what happens in a sore muscle

When you exert yourself in a way your body isn't used to — a new gym class, the first run after the holidays, a padel match that went on too long, walking down a mountain — the muscle fibers suffer small injuries. It is especially eccentric contractions, those in which the muscle works while lengthening (going down stairs, braking the descent of a weight, running downhill), that leave this "signature".

What follows is a perfectly normal, but uncomfortable repair response:

• In the first few hours, the muscle may only feel tired. Pain is almost non-existent.
• Between 24 and 72 hours, the peak arrives. The area becomes sensitive to touch and movement, strength decreases, and simple actions — sitting down, raising your arms, picking up a child — become difficult.
• From then on, the pain gradually disappears, but strength may take longer to return to normal.

Behind this sequence are three processes worth knowing, because they are exactly the ones where red light seems to intervene:

1. Local inflammation — the body recruits cells and inflammatory mediators to clean and repair the tissue. It is useful, but when it is prolonged or excessive, it increases pain and swelling.
2. Oxidative stress — intense exercise increases the production of reactive oxygen species. In small doses, they are useful signals; in excess, they damage cellular structures.
3. Energy deficit — repairing fibers costs energy (ATP). A tired and injured muscle has to do more with less.

DOMS is not a sign of serious injury or a badge of a good workout. It is simply the cost of asking your body to do something new. The problem is that this cost is paid the next day — at work, at home, in the workout that gets postponed.

How red light "talks" to a sore muscle

Red light therapy, or photobiomodulation (PBM), uses visible red light and near-infrared (NIR) with specific wavelengths. Unlike ultraviolet light, it doesn't tan or burn; and unlike a sauna, the goal is not to heat, but rather to trigger a biological response.

The mitochondrion as a light receptor

The most studied target is an enzyme called cytochrome c oxidase, the final piece of the respiratory chain inside the mitochondria — the structures that produce the cells' energy. Researcher Tiina Karu, one of the pioneers in this area, described this enzyme as the main "photoreceptor" of red light and near-infrared light in mammalian cells.

The most accepted explanation, reviewed by Michael Hamblin (Harvard Medical School), is the following: in cells under stress — such as those of an injured muscle — nitric oxide (NO) binds to cytochrome c oxidase and acts as a brake on cellular respiration. Light helps release this NO. The result is a cascade of effects:

• More ATP: the mitochondrion efficiently uses oxygen again and produces more energy for repair processes.
• Free nitric oxide: once released, NO is also a vasodilator, which can favor local circulation.
• A brief and controlled oxidative signal: a small increase in reactive oxygen species that, instead of damaging, activates genes linked to repair and antioxidant defenses.
• Modulation of inflammation: according to Hamblin's review on the anti-inflammatory effects of photobiomodulation, light tends to reduce pro-inflammatory mediators and oxidative stress markers in several experimental models.

Notice the irony: exercise injures the muscle through oxidative stress and inflammation, and photobiomodulation seems to act precisely on these two processes — not canceling them out (which could impair training adaptation), but helping to "turn down the volume".

660 nm or 850 nm: how far does the light reach?

Not all light reaches the same place. Visible red (in the 630–670 nm range, for example 660 nm) is absorbed mainly in the most superficial layers — skin and surface tissues. Near-infrared (810–850 nm, and even further at 1060 nm) is almost invisible to the human eye, but penetrates more deeply, reaching muscles and joints.

For those who want to recover a quadriceps or calves, this is decisive: near-infrared is what has the best chance of reaching the muscle fibers. It is no coincidence that Vanin and colleagues' review (2018) found positive results mainly in a range between 655 and 950 nm — red and near-infrared together.

More is not better: the biphasic response

There is a detail that separates those who understand photobiomodulation from those who just "turn on a light": the response is biphasic. A dose that is too low does nothing; an adequate dose stimulates; an excessive dose can cancel the benefit. This phenomenon was described by Huang, Hamblin, and colleagues in a review published in the journal Dose-Response. In practical terms: staying twice as long in front of the panel does not double recovery. That is why distance and time protocols exist — and it is advisable to respect them.

The new meta-analysis: what changes after 72 hours

Let's then go to the study that gave rise to this article.

Zhao and colleagues (2026), Science & Sports — "Can photobiomodulation therapy attenuate delayed-onset muscle soreness and strength loss after exercise in healthy individuals or athletes? A meta-analysis of randomized controlled trials".

The team searched six scientific databases (PubMed, Web of Science, Scopus, Medline, Embase, and SportDiscus) up to April 2026 and started with 5597 records. After eliminating duplicates and studies that did not meet the criteria, 13 randomized clinical trials with healthy people or athletes remained. The novelty was analyzing the time factor: what happens immediately after exercise, at 24, 48, 72, and 96 hours.

What they found:

• Perceived pain (visual analog scale): statistically significant differences in favor of photobiomodulation immediately after exercise and at 24 hours.
• Pressure sensitivity (algometry): significant differences immediately after exercise and at 48, 72, and 96 hours.
• Strength (peak torque): higher values in the photobiomodulation group immediately after exercise and at 24, 48, 72, and 96 hours.
• Dose: for pain, several doses had an effect; for strength, the higher doses seemed to give better results.

The authors' conclusion: photobiomodulation can reduce the level of DOMS in the 72 hours following exercise and increase the level of strength up to 96 hours.

Impartial reading: it is a recent and methodologically structured meta-analysis (risk of bias assessment by Cochrane and certainty of evidence by the GRADE method), but it combines studies with different devices, doses, and types of exercise, and most trials in this area have small samples. It is a strong sign that it is worth taking light seriously in recovery — not a guarantee of results for everyone.

What other studies had already shown

The 2026 meta-analysis does not come out of nowhere. It joins more than a decade of research, much of it done by groups in Brazil, the United States, and Europe.

Performance and recovery markers

Leal-Junior et al. (2015), Lasers in Medical Science. Systematic review with meta-analysis of trials with low-intensity laser and LED. Of the 13 trials of acceptable quality, 12 applied the light before exercise. Phototherapy increased the number of repetitions and the time to exhaustion, and most comparisons showed positive results in markers such as creatine kinase (CK), an indicator of muscle injury. The most consistent results came from red or infrared light applied before the effort.

Vanin et al. (2018), Lasers in Medical Science. A larger review: 39 trials and 861 participants. It found some effect in favor of photobiomodulation on time to exhaustion, number of repetitions, peak torque, and lactate — but classified the quality of evidence as very low to moderate, calling for better and more standardized studies.

From the laboratory to the human muscle

Ferraresi, Huang, and Hamblin (2016), Journal of Biophotonics. Review of 46 studies (1045 participants) with athletes and non-athletes. The authors describe that light applied before (preconditioning) or after exercise can improve performance and that, in muscle biopsies, photobiomodulation was associated with less inflammation and less oxidative stress. They even ask if the technique should be allowed in competition.

Ferraresi et al. (2016), American Journal of Physical Medicine & Rehabilitation. An unusual case: two identical twins, the same strength training plan for 12 weeks, one with 850 nm LED after each session and the other with a placebo. The twin treated with light lifted more weight, had less fatigue, lower CK values, and less delayed muscle soreness, in addition to changes in genes linked to inflammation and protein synthesis. It is just a pair of people — it does not allow generalization — but it illustrates the mechanism well.

Light vs. ice and other therapies

Ferlito et al. (2022), Lasers in Medical Science. Directly compared photobiomodulation with cryotherapy (ice, cold water immersion) after intense exercise. In four trials (66 participants), photobiomodulation was associated with more strength, less DOMS, and fewer muscle injury markers than cryotherapy, with no differences in inflammation or oxidative stress. The certainty of evidence was classified as moderate to very low.

Chen et al. (2025), Journal of Pain Research. A network meta-analysis compared several physical therapies for DOMS. At 24 hours, only photobiomodulation showed a significant advantage over the placebo; at 48 hours, photobiomodulation and the sauna. After 48 hours, no therapy clearly distinguished itself from the placebo. A useful reminder: the window that seems to matter most is the first two days.

The other side: when light made no difference

An honest article must also show the studies that found no effect:

• Zagatto et al. (2020) applied whole-body photobiomodulation to water polo players after official matches. With the parameters used, they did not find faster recovery of inflammation, muscle injury markers (except one, LDH), hormones, or strength.
• Do Nascimento et al. (2024) tested LED before a 5 km run in recreational runners, with three different doses. The race time and perceived exertion were equal to the placebo.
• Borim et al. (2025) did the same with female futsal players: none of the doses improved strength, power, or immediate muscle endurance.

What does this tell us? That photobiomodulation is not an instant "turbo" for the performance of a race day. The most consistent results appear in recovery — pain, strength in the following days, injury markers — and depend heavily on the dose, wavelength, and type of effort. That is also why the evidence on pain continues to be considered mixed: light can be a good complement, but it does not replace rest, nutrition, sleep, or physical therapy.

Before or after the workout? The question almost no one asks

Most users turn on the panel after the workout, when the pain is already on its way. But research has opened another possibility: muscle preconditioning — applying the light before the effort, to prepare the muscle.

Vanin et al. (2016), Lasers in Medical Science. In this randomized, double-blind, placebo-controlled trial, 48 men between 18 and 35 years old did 12 weeks of strength training. The groups received active light or placebo before and/or after each session. The group that received the light before the workout (and placebo after) had the greatest strength gains in maximum contraction and 1-repetition maximum tests.

Combining this trial with Leal-Junior's review, the message is interesting: for performance and strength gains, light before the workout has more support; for comfort and recovery, the session after the effort still makes sense — and was, in fact, the time used in the study of the twins. Many people end up alternating depending on the goal of the week. The most important thing is to choose a time that you can maintain consistently.

After 40: when recovery becomes the real workout

At 25 years old, DOMS is a curiosity. At 45, it can be the reason to give up. With age, muscle mass and strength tend to decrease, and many amateur athletes feel they need more days to recover from the same effort. Just one week of pain is enough to break the routine — and routine is everything.

Research in older people is still limited, but there are encouraging signs. Toma et al. (2016), also in Lasers in Medical Science, followed elderly women during 8 weeks of strength training. The group that combined the training with infrared laser (808 nm) had more work, peak torque, and power than the control group without training. It is not a study on DOMS, and the participants were much older than most weekend athletes, but it shows that the aging muscle also responds to light when it is combined with exercise.

For those who are 40, 50, or 60 years old and want to continue running, swimming, playing padel, or lifting weights, the question stops being "how much can I train?" and becomes "how much can I recover?".

The "next day": the pain that goes with you to work

There is a dimension of DOMS that almost no one talks about: the normal days. The meeting where you cannot sit without discomfort. The subway stairs. The Thursday workout that gets postponed because your legs haven't recovered from Tuesday's. The bad mood of someone who feels "old" after a single game.

And there is sleep. Muscle pain can make it difficult to rest, and worse sleep slows down recovery — a cycle that is not very pleasant. Many people integrate a red light session at the end of the day, in a calm environment without screens, as part of a recovery ritual. We talked about the relationship between red light and sleep in a recent article on our blog; here is just the main idea: sleep continues to be the most powerful recovery tool that exists, and no panel replaces it.

Common problems that a panel at home can help minimize

Based on the studies above, these are the scenarios where photobiomodulation has the most support as a complement:

• DOMS after new or more intense workouts — the most recent evidence points to less pain in the first 24 to 72 hours.
• Loss of strength in the following days — the 2026 meta-analysis found more strength up to 96 hours.
• Elevated muscle injury markers (such as CK) — several reviews show a trend towards lower values.
• Muscle fatigue — more repetitions and more time to exhaustion in several trials, especially with the light applied before the effort.
• Overloaded and localized areas — calves, quadriceps, lower back, shoulders, forearms of padel or tennis players.
• Lack of time to recover — a few minutes at home, without travel, that fit at the end of a workout or in the evening routine.

How to use a panel at home: a practical protocol

These are general wellness and equipment use guidelines, not a medical prescription. Always follow your equipment manual.

• Distance: about 15 cm between the panel and the skin.
• Bare skin: thick clothing blocks the light; the area to be treated must be exposed.
• After intense effort: 15 to 20 minutes per muscle group, in a session after the workout.
• Regular recovery: 10 to 15 minutes per muscle group, 2 to 5 times per week.
• Combination of spectra: for muscle, include near-infrared (for example, 850 nm), preferably combined with red.
• Interval between sessions: at least 6 hours.
• Start with the lower limit of time and increase only if it is well tolerated — remember the biphasic response.
• Consistency: several sessions over the weeks count more than a single long session.
• Do not give up on the rest: hydration, sufficient protein, sleep and progressive training loads continue to be the foundation.

Some precautions before starting

Photobiomodulation has a very favorable safety profile in published studies, and that is precisely why it is worth using it with common sense. Use the included protective glasses, especially if you are sensitive to intense light. If you have photosensitivity, take photosensitizing medication, have a disease that causes light sensitivity or a recent sunburn, talk to your doctor first. Avoid applying the light over suspicious lesions, over areas with active oncological disease and, during pregnancy or breastfeeding, do not use without medical guidance. If muscle pain is intense, unusual, accompanied by marked swelling or dark urine, or does not improve after a few days, it is not "normal" DOMS — seek a healthcare professional. In case of injury, light can be a complement to physiotherapy, never a substitute.

Frequently asked questions

Does red light eliminate muscle pain?

It does not eliminate it. Studies suggest that it can help reduce the intensity of delayed-onset muscle soreness, especially in the first 24 to 72 hours, and recover strength faster. The effect varies from person to person and depends on the dose and wavelength.

Is it better to use the panel before or after the workout?

It depends on the goal. For performance and strength gains, studies that applied the light before the workout showed more consistent results. For recovery and comfort, a session after the effort is the most intuitive and practical option. What matters is consistency.

Can I use red light instead of ice?

A 2022 meta-analysis found better results with photobiomodulation than with cryotherapy in strength and DOMS, but with few studies. They are not incompatible — and neither replaces rest.

How many times a week should I use it?

For muscle recovery, 2 to 5 times per week, with 10 to 15 minutes per muscle group at about 15 cm, and at least 6 hours between sessions. After a very demanding workout, a session of 15 to 20 minutes per muscle group.

Does it make sense for non-athletes?

Yes. DOMS affects especially those who make efforts they are not used to — those who are starting, returning after a break or trying a new sport. That is precisely where recovery matters most.

TheraFactor®'s approach to recovery

At TheraFactor®, we believe that recovery is not a luxury for professional athletes — it is what allows anyone to continue training next month, next year and next decade.

It was with this in mind that we developed the TheraPRO line:

• 8 therapeutic wavelengths — 630, 650, 660 and 670 nm in red and 810, 830, 850 and 1060 nm in near-infrared — to work from the surface to the deepest layers, where the muscles are.
• DualPRO+ Chip: high-precision dual diodes that emit two spectra per LED.
• Independently adjustable spectra, pre-defined protocols (including a muscle program), touch panel and control via the TheraFactor® app.
• Ultra-low EMF, below 1 mG.
• Three sizes for three realities: the TheraPRO 120, compact and portable (3.9 kg), with included articulated arms — ideal for localized areas such as calves, knee, shoulder or lower back; the TheraPRO 300, for larger areas of the body; and the TheraPRO 600, for maximum coverage at home. The 300 and 600 include a wheeled floor base, free of charge.
• Cascade connection: the panels can be connected to each other and work as one, to cover legs and torso at the same time.
• 3-year warranty, 60-day satisfaction and free delivery.

ATTENTION: Common light panels do not have the power, nor the right wavelength to activate mitochondria. TheraPRO Panels from TheraFactor®️ use high-precision dual diodes, protected against EMF and with exact emission in the therapeutic ranges.

Your next workout starts with the recovery from the previous one

Think about the last workout that cost you two days. Not the pain itself, but what was left undone: the postponed run, the game you didn't go to, the feeling that your body no longer keeps up with your will. Most people accept this as the price of "no longer being 20 years old". And they train less and less — not for lack of motivation, but because recovery has never had the same attention as training.

There are more and more people in Portugal — weekend runners, padel players, those who returned to the gym after 40 — who are already part of another group: those who treat recovery as part of the plan. A few minutes, at home, after the effort.

If you already invest time, money and willpower in your body, maybe it is time to stop asking it to recover on its own. Discover the TheraPRO line at therafactor.eu — and take advantage of the 5% discount that the online store always has available. Thursday's workout will thank you.

References

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2. Leal-Junior EC et al. Effect of phototherapy (low-level laser therapy and light-emitting diode therapy) on exercise performance and markers of exercise recovery: a systematic review with meta-analysis. Lasers Med Sci. 2015;30(2):925-39. PubMed 24249354
3. Vanin AA et al. Photobiomodulation therapy for the improvement of muscular performance and reduction of muscular fatigue associated with exercise in healthy people: a systematic review and meta-analysis. Lasers Med Sci. 2018;33(1):181-214. PubMed 29090398
4. Ferraresi C, Huang YY, Hamblin MR. Photobiomodulation in human muscle tissue: an advantage in sports performance? J Biophotonics. 2016;9(11-12):1273-1299. PubMed 27874264
5. Ferraresi C et al. Effects of Light-Emitting Diode Therapy on Muscle Hypertrophy, Gene Expression, Performance, Damage, and Delayed-Onset Muscle Soreness: Case-control Study with a Pair of Identical Twins. Am J Phys Med Rehabil. 2016;95(10):746-57. PubMed 27088469
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9. Toma RL et al. Low level laser therapy associated with a strength training program on muscle performance in elderly women: a randomized double blind control study. Lasers Med Sci. 2016;31(6):1219-29. PubMed 27250715
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12. Borim JM et al. Acute dose-response effect of photobiomodulation therapy on muscle performance in female futsal players: A randomized, double-blind, placebo-controlled, crossover study. J Bodyw Mov Ther. 2025;41:35-43. PubMed 39663094
13. Karu TI. Multiple roles of cytochrome c oxidase in mammalian cells under action of red and IR-A radiation. IUBMB Life. 2010;62(8):607-10. PubMed 20681024
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