Making sense of the research behind red light therapy

Most of us have experienced the soreness that can appear a day or two after unfamiliar or demanding activity.

It’s often called delayed onset muscle soreness, or DOMS.

A 2025 systematic review examined 14 studies investigating photobiomodulation following exercise induced muscle soreness.

When the researchers combined the available data, they found reductions in soreness at 72 and 96 hours, as well as improvements in muscle strength during the earlier stages of recovery.

The findings help explain why muscle soreness and recovery have become such active areas of photobiomodulation research.

For people who want to remain active, recovery isn’t simply about feeling comfortable after exercise.

It’s also about how well the muscles regain their ability to work again.

These findings suggest photobiomodulation can play a useful role in supporting muscle recovery, including soreness and the return of muscle strength after demanding activity.

An interesting part of photobiomodulation research is that the light isn’t always used after physical activity.

A 2025 systematic review and meta-analysis examined different approaches to muscle recovery and included 19 studies involving 672 participants.

The researchers found that photobiomodulation applied before exercise reduced muscle soreness and improved muscle performance 24 hours after exercise induced muscle damage.

The evidence for reduced soreness was rated as low certainty, so further research will help refine the most effective treatment approaches.

We often think about recovery as something that begins once exercise is over.

This research suggests the story may be more interesting than that.

Photobiomodulation is being investigated not only as something used after activity, but also as a way of supporting the muscles before they’re challenged.

Recovery may begin earlier than we think.

Muscle fatigue is that familiar point where muscles become less able to keep doing the work we’re asking of them.

A systematic review and meta-analysis looked at photobiomodulation and functional performance in 16 studies involving 340 healthy people.

The researchers found that PBM helped with fatigue recovery.

They didn’t find evidence that photobiomodulation on its own increased muscle strength or overall functional capacity.

We think this distinction is important.

Red light therapy isn’t creating strength without exercise.

Instead, the research suggests its more interesting role may be around how muscles respond to activity and recover from fatigue.

That fits with the way we think about photobiomodulation generally:

Supporting the body doesn’t mean replacing the work the body still needs to do.

Researchers have also looked at whether photobiomodulation used before exercise can influence muscle endurance and subsequent recovery.

A 2024 meta-analysis brought together randomised controlled trials involving both trained and untrained people.

The results suggested that PBM used before exercise could improve muscle endurance and support recovery of muscle strength and markers associated with muscle damage.

The size of the effect varied depending on the activity level of the participants.

What makes these findings particularly interesting is the effect on muscle endurance and recovery.

The research suggests photobiomodulation may influence how long muscles can continue working and how they recover after being challenged.

That’s one reason timing has become such an interesting part of PBM research.

Photobiomodulation has also been studied as a way of supporting different types of physical performance.

A 2022 systematic review and meta-analysis included 37 studies and 586 participants.

The researchers found improvements in some specific measures, including single joint muscle endurance and cycling time to exhaustion.

But benefits weren’t found across every type of exercise.

For example, the review didn’t find improvements in muscle strength, running performance or swimming time trial performance.

“Physical performance” isn’t one single thing.

Strength, endurance, sprinting and prolonged exercise all place different demands on the body.

The research suggests photobiomodulation may be more useful for some aspects of performance than others.

For us, the most interesting part isn’t whether red light can make someone a faster athlete.

It’s what this research may teach us about muscle endurance, fatigue and recovery.

For photobiomodulation to produce a biological response, light first needs to interact with molecules within our cells.

One of the leading mechanisms researchers have investigated involves cytochrome c oxidase, an enzyme found within mitochondria.

When particular wavelengths of red and near-infrared light are absorbed, researchers believe this interaction can influence processes involving cellular energy, signalling molecules and other biological responses.

Those initial changes may then trigger a cascade of activity within the cell.

The important idea is surprisingly simple:

Light can carry information that living cells respond to.

Photobiomodulation isn’t simply about warming tissue or producing a bright red glow.

The light itself can interact with biological systems.

Scientists are still investigating exactly which mechanisms are most important, and cytochrome c oxidase isn’t necessarily the only photoacceptor involved.

But understanding these cellular interactions gives us the foundation for understanding PBM.

Mitochondria are tiny structures found inside most of our cells.

They’re often described as the cell’s “powerhouses” because one of their important jobs is helping produce ATP, a molecule cells use to power many of their activities.

But mitochondria do much more than simply produce energy.

They also participate in cellular signalling and help cells respond to changes in their environment.

A 2024 review of photobiomodulation mechanisms describes how red and near-infrared light may influence mitochondrial activity and downstream processes involving ATP, reactive oxygen species, nitric oxide, calcium and cellular signalling.

You’ll sometimes hear red light therapy described as simply “giving your cells more energy.”

We think that’s a little too simplistic.

The more interesting story is that light may influence mitochondrial activity and initiate signals that affect the way cells behave and respond.

Mitochondria aren’t simply batteries being recharged. They’re part of a much more complex biological conversation.

And researchers are still working to understand that conversation.

Not all light behaves the same way when it reaches the body.

The wavelength of light influences how it interacts with tissue and how deeply some of that light may travel.

Visible red light generally interacts more superficially, while longer near-infrared wavelengths can penetrate further into tissue.

But there isn’t one fixed depth for a particular wavelength.

Research examining the penetration of visible and near-infrared light through different tissues shows just how much penetration can vary according to factors such as wavelength, tissue thickness and the anatomical area being treated.

This is why statements such as:

“850nm penetrates exactly X centimetres” can be misleading.

The human body isn’t a uniform block of material.

Skin, fat, muscle, bone and other tissues interact with light differently.

A more useful way to understand it is:

Red light generally acts more superficially.

Near-infrared light can reach deeper tissues.

That’s also one reason many photobiomodulation devices combine red and near-infrared wavelengths.

It’s tempting to assume that if some red light is useful, more must be better.

Photobiomodulation doesn’t appear to work that way.

Researchers have observed what is known as a biphasic dose response.

In simple terms, there may be a useful range of light exposure where a biological response occurs.

Too little may not produce enough of a response.

But once an effective range has been reached, continuing to increase the dose doesn’t necessarily produce a greater benefit and may sometimes reduce the desired response.

A major review of PBM dosing research examined this phenomenon across laboratory, animal and clinical studies.

This is one of the most useful concepts for anyone using red light therapy to understand.

More isn’t necessarily better. The right amount matters.

And “the right amount” isn’t one universal number.

Dose depends on several things, including wavelength, irradiance, treatment time, distance from the light and the tissue or condition being studied.

That’s why we encourage people to follow the instructions for their particular device rather than simply using the highest intensity for the longest possible time.

One of the most fascinating things about photobiomodulation is that the light interaction itself is only the beginning.

Once light has been absorbed by cellular molecules, researchers have observed changes involving things such as ATP, nitric oxide, reactive oxygen species and calcium signalling.

Those changes can influence signalling pathways inside the cell.

In other words, a relatively small interaction involving light may initiate a much larger biological response.

Exactly which pathways dominate can depend on the cells, tissue, dose and circumstances being studied.

This helps explain why researchers study PBM across such different areas of the body.

They’re not suggesting that red light somehow has a separate magical effect for every condition.

They’re investigating whether an interaction with light can influence fundamental cellular processes that occur throughout the body.

That’s a very different idea.

Light → Cellular interaction → Biological signal → Cellular response

And from there, researchers investigate what those responses may mean in different tissues and different health conditions.