One of the lesser known parts of the body that light therapy studies have examined is the muscles. Human muscle tissue has highly specialised systems for energy production, needing to be able to provide energy for both long periods of low consumption and short periods of intense consumption. Research in this area has accelerated dramatically in the last couple of years, with dozens of new high quality studies every month.
Red and infrared light have been proven useful for a variety of ailments and conditions, from joint pain to wound healing, because the cellular effects work on a foundational energetic level. So if light penetrates down into muscle tissue, can it exert beneficial effects there? In this article we will examine how light interacts with these systems and what benefits it may bring.
Light improves muscle function, but how?
To understand how light might affect muscle tissue, we need to first understand how muscle tissue actually functions.
Energy is necessary for life in every cell of every species we currently know of. This fact of life is more obviously apparent in muscle tissue, from a mechanical perspective, than any other type of tissue. Since muscles are involved in movement, they must be generating and using energy, or they wouldn’t move. Anything that helps with this fundamental energy production will be valuable.
- The light therapy mechanism
Light therapy has a well-known mechanism in any nearly any cell of the body with a mitochondrion (mitochondria being the organelles responsible for energy production). You can look into Cytochrome C Oxidase and Nitric Oxide to learn more of the specifics here, but basically, both red and near-infrared light help our mitochondria to complete the process of respiration, giving more CO2 and ATP (energy). This applies in pretty much any cell of body, besides those lacking mitochondria such as red blood cells.
- The muscle-energy connection
One of the key characteristics of muscle cells is that they are exceptionally abundant in mitochondria, needing them to fulfil the high energy demands. This applies to skeletal muscle, cardiac muscle, and smooth muscle tissue like you would find in internal organs. The density of mitochondria in muscle tissue varies between species and parts of the body, but they all need a high degree of energy to function. The rich presence overall suggests that light therapy has great potential to affect muscles, even more so than it can affect other tissue.
- Muscle stem cells – growth & repair enhanced by light
Myosatellite cells, a type of muscle stem cell involved in growth and repair, are also a key target of light therapy1,5, perhaps the main target that gives long term effects. These satellite cells become active in response to strain (such as from mechanical movement like exercise or from injury) – a process that is enhanced by light therapy9. Like stem cells in any location of the body, these satellite cells are essentially the precursors to normal muscle cells. They usually exist in a relaxed, inactive state, but will turn into other stem cells or turn into fully functional muscle cells as part of the healing process, in response to injury or exercise trauma. Recent research points to mitochondrial energy production within stem cells as the primary regulator of their fate6, essentially determining their ‘programming’ as well as their speed and efficiency. Since light therapy is a potent promoter of mitochondrial function, a clear mechanism exists to explain how light improves our muscle growth and repair via stem cells.
Inflammation is a typical feature associated with muscle damage or stress. Light will help to reduce the severity of the inflammation3 (by increasing levels of CO2 – which then goes on to inhibit inflammatory cytokines/prostaglandins), thus allowing more efficient repair without scarring/fibrosis5.
Light therapy can also help muscles indirectly by:
- Thyroid regulation
Considered by some as the master regulatory hormone of the body, thyroid hormones are involved in cellular energy production in a big way. As mentioned above energy production is essential for both muscular performance and recovery. Studies indicate that (near)infrared light can be used on the thyroid gland to help normalise thyroid hormone levels, thus helping muscle performance downstream. You can read more about thyroid light therapy here.
- Sleep improvement
Better sleep is one of the most often reported effects of red light therapy, with several studies now showing evidence to support the common claim. As bodybuilders and athletes will testify to, good deep sleep is one of the most important parts of recovery, so any improvement here will help muscle function and healing.
- Testosterone boost
For men, red light can be used directly on the testes to improve levels of the hormone testosterone. This hormone is well established in endocrinology as directly useful in boosting muscle strength, size and performance. We have a whole blog post on this topic here.
The benefits to muscle function from light therapy
Essentially anyone that uses their muscles will see benefits from light therapy – athletes10,11,12,16,18, people with injuries and muscular disorders, bodybuilders20, and even just regular people exercising to stay in shape2,17. The same applies to pretty much any animal too, such as horses and dogs, whether involved in competitive racing or otherwise. Light therapy offers a side-effect free treatment to improve performance and recovery without having to use drugs. Below are several key benefits you can expect from using light therapy on muscles:
The increase in size of muscles as a result of exercise (known as hypertrophy) has been studied in conjunction with light therapy, with interesting results2,14. In the context of muscle tissue, hypertrophy is part of an adaptive response that helps the tissue to generate more force with less fatigue. The physical appearance of long term gains in muscle size is highly sought after by bodybuilders and anyone trying to improve their shape/physique.
There is clear evidence that using near-infrared light before weight training improves hypertrophy and muscle size gains significantly compared to doing the same weight training exercises without any light. In a group of untrained people, weight training with light therapy was associated with a doubling in muscle size gains over a period of 8 weeks, compared to doing the same exercise without any light therapy.
This makes light therapy a highly effective tool for personal trainers10, or for elite athletes exercising alone11,12,16,18, or even just for regular people especially after a period of being sedentary2, potentially doubling your first few month’s progress, and being an aid in the long term too.
This effect applies to skeletal muscles in pretty much any location on the body – biceps, quads, etc. Although this specific study was done on untrained individuals, there is reason to believe it will be effective for even well trained athletes10,11,18, adding a big edge to exercise results.
Strength – get stronger with light therapy
Briefly mentioned above, light will interact with Myosatellite cells and regular muscle cells by improving energy production. This gives an immediate increase in strength and endurance through the regular muscle cells12,13,14,20, but also a long term increase through the myosatellite cells (relative to exercising without any complimentary light therapy)4.
The studies looking at this tend to examine peak torque – the maximum force generated by a specific movement – and how this changes over time. Just like with hypertrophy, or to some extent because of hypertrophy, light therapy in conjunction with exercise will clearly improve your gains in strength compared to exercise alone2. The gains are so significant across a wide range of studies that international regulatory authorities for sports are considering whether light therapy should even be permitted10.
Reduce DOMS/soreness with light therapy
Several studies on muscle light therapy now point to the reduction, and quicker resolution, of delayed onset muscle soreness4,14 – the uncomfortable, yet sometimes satisfying, feeling you get in muscles the day after a tough workout.
DOMS is thought to be caused by microtrauma to muscle fibers and is characterised on a cellular level by a rapid influx of calcium into the cell (amongst other things), which inhibits respiration. The displaced calcium entering the muscle cells can lead to damage and inflammation, hence the painful/sore feeling.
The calcium needs to be transported out of the cell again for recovery to proceed, and the cell needs ATP (energy) to do this. Fortunately the main light therapy mechanism is to speed up production of ATP (not to mention helping us to produce CO2 which reduces inflammation), and thereby speeds up the whole muscle recovery process7,8,9, reducing both the severity of DOMS and the length of time until full recovery.
Improve injury/strain recovery with light
Various studies point to the dramatically positive effects of light on post-injury recovery3,4,7,9. One risk of muscle injuries in general is the formation of fibrosis or scar tissue. Just as we get scars on the skin as a result of damage, we can also get them inside the muscles as the inflammatory response causes a spike in collagen formation. Light therapy will help to prevent that scarring5.
When scar tissue forms in muscles, this permanently alters the function and mechanical properties of the muscle, leading to reduction in mobility/strength, long term pain, perhaps ending an athlete’s career or even disability in extreme cases. Resolving the injury as quickly as possible with as little inflammation as possible is crucial.
Light therapy seems especially effective here for several reasons – as mentioned above it is highly effective in reducing the acute inflammatory response, but also in kick starting and supporting the key processes of the muscle recovery process on a cellular level. Indeed this healing effect from light therapy is apparent on not just muscle injuries, but wounds anywhere on the body, such as the skin but even brain trauma and broken bones.
Ideal light for muscle light therapy
There are several factors to consider to ensure that your light device is suitable for muscle light therapy.
- Infrared penetrates more than red
Perhaps the most obvious barrier to successful light therapy on muscles is actually getting the light down into the muscles. The majority of light applied to the body is absorbed in the skin, making treatment of deeper tissue problematic.
Fortunately, we know that the infrared light therapy wavelengths between about 700-900nm penetrate much better than other wavelengths, including the red wavelengths at 600-700nm. This makes near-infrared light by far the best choice for muscle treatment. This doesn’t include any other form of infrared light, such as the mid-infrared or the far-infrared heat, neither of which are at all suitable. Even the near-infrared over 900nm is not really suitable, since it is progressively blocked by water in skin cells. You basically want near-near-infrared.
Red light can still be used, but will need a much higher application dose compared with an equal dose of infrared. Red light around 660-670nm is actually used in a large amount of studies on the topic, referenced below, especially in smaller animals like rodents, where penetration is less of an issue due to their tiny size. It still gives good effects. 760-780nm is used in quite a few studies too, showing equally good effects. Most of the studies seem to indicate light around 810-830nm as the most useful range17,18,19, especially in larger animals like humans.
- Higher power density / high dose required
Even using the most penetrative types of near-infrared light at about 830nm, most of the energy is still absorbed by the skin and first layers of tissue (albeit a lower percentage than other wavelengths). So once you have ensured your light device has the suitable wavelengths, you need to ensure the right power. A low light intensity of even the most ideal wavelength of light isn’t going to do much good.
So to build up a suitable dose of light in muscles, especially deep into the large muscles in the arms and legs, you need a strong light and you need to apply it for a long time. In terms of light strength, below 50mW/cm² is definitely too weak for muscle depth penetration in humans. 200mW/cm² or more are indicated for sufficient energy penetration in reasonable time frames2,15.
Doses of 100J/cm² or more, even up to 700J/cm², are indicated for penetrating into deeper muscles with sufficient energy over time. If you want to know more about light therapy dosing, see this post here.
- Before or after exercise?
One you have a light device with the correct wavelengths and enough power output, you need to figure out the best time to apply the dose. Studies at the moment indicate superior results when light is used before exercise4,11,15. This is also the conclusion is several literature reviews and meta-analyses on the subject. Using light therapy this way seems to improve not only exercise performance (strength, speed, endurance) but also muscle recovery post-exercise. It makes sense that using it this way will also reduce the chance of injury.
Using light after exercise is still effective for recovery however, and much better than no light at all. Even using light several hours after exercise is helpful.
It could be that using light on the target muscles both before and after exercise is the best method, although this protocol has not been thoroughly compared to other protocols.
- What light specifically?
All of the studies on the topic of muscle light therapy, and indeed the light therapy field in general, use either LEDs or lasers, both of which seem to be equally effective, with minor variations in parameters. This type of energy efficient, heat free, and specific wavelength lighting technology is required for muscle light therapy for various reasons.
As the muscles are deep within the body, high doses of light must be applied to the skin in order for a reasonable dose to reach the actual muscle tissue. If a less specific lighting technology such as heat lamps, ‘infrared bulbs’, incandescents and other broad spectrum lights are used for the same purpose, a truly ridiculous amount of energy would have to be applied to skin to ensure the muscles receive a good dose, resulting in severe overexposure. Using these types of lights at a range that gives a good power density of the penetrative 700-850nm wavelengths would also burn the skin almost immediately.
Stick to LEDs or laser technology for light therapy that will actually penetrate to the relevant deep tissue.
- Light therapy helps muscles in a variety of ways
- Exercise recovery, injury recovery, muscle strength/endurance, hypertrophy, pain reduction and more.
- Red and near-infrared light (600 – 900nm wavelengths) works on muscle cells and muscle stem cells by improving energy production, reducing inflammation and speeding healing.
- Effects are especially important for recovery from muscle injuries, maximizing the chance of full recovery without degradation in function. Also gives a huge boost in gains to people just starting exercising, making it a useful tool for personal trainers.
- Near-infrared (at 760-830nm wavelengths) is the most effective range, due to the superior penetration.
- Still requires a high power density of light (200mW/cm² or more) to achieve the penetration in bigger muscles.
- LEDs and lasers are the only currently viable, studied devices. Heat lamp light does not penetrate to muscles in sufficient density.
- Light therapy is best used BEFORE exercise to maximise results, rather than after, according to current information.
- Low-level laser (light) therapy (LLLT) on muscle tissue: performance, fatigue and repair benefited by the power of light. Cleber Ferraresi et al. 2012
- Effect of low-level laser therapy on muscle adaptation to knee extensor eccentric training. Baroni BM et al. 2015
- The low-level laser therapy on muscle injury recovery: literature review. Daniel Rodrigues dos Santos et al. 2010
- Does Phototherapy Enhance Skeletal Muscle Contractile Function and Postexercise Recovery? A Systematic Review. Paul A Borsa et al. 2013
- Low-level laser therapy (808 nm) contributes to muscle regeneration and prevents fibrosis in rat tibialis anterior muscle after cryolesion. Assis L et al. 2013
- Mitophagy-driven mitochondrial rejuvenation regulates stem cell fate. Vazquez-Martin A et al. 2016
- Red and Infrared Low-Level Laser Therapy Prior to Injury with or without Administration after Injury Modulate Oxidative Stress during the Muscle Repair Process. Ribeiro BG et al. 2016
- Effects of low-level laser therapy on ROS homeostasis and expression of IGF-1 and TGF-β1 in skeletal muscle during the repair process. Luo L et al. 2013
- Effects of low-level laser therapy on skeletal muscle repair: a systematic review. Alves AN et al. 2014
- Photobiomodulation in human muscle tissue: an advantage in sports performance? Ferraresi C et al. 2016
- Muscular pre-conditioning using light-emitting diode therapy (LEDT) for high-intensity exercise: a randomized double-blind placebo-controlled trial with a single elite runner. Ferraresi C et al. 2015
- Photobiomodulation Therapy Improves Performance and Accelerates Recovery of High-Level Rugby Players in Field Test: A Randomized, Crossover, Double-Blind, Placebo-Controlled Clinical Study. Pinto HD et al. 2016
- Light-emitting diode therapy in exercise-trained mice increases muscle performance, cytochrome c oxidase activity, ATP and cell proliferation. Ferraresi C et al. 2016
- 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. Ferraresi C et al. 2016
- 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. Leal-Junior EC et al. 2015
- Comparison between cold water immersion therapy (CWIT) and light emitting diode therapy (LEDT) in short-term skeletal muscle recovery after high-intensity exercise in athletes–preliminary results. Leal Junior EC et al. 2011
- Effect of 830 nm low-level laser therapy in exercise-induced skeletal muscle fatigue in humans. Leal Junior EC et al. 2009
- Effect of 830 nm low-level laser therapy applied before high-intensity exercises on skeletal muscle recovery in athletes. Leal Junior EC et al. 2009
- 830 nm light-emitting diode (led) phototherapy significantly reduced return-to-play in injured university athletes: a pilot study. Foley J et al. 2016
- Near-infrared light therapy to attenuate strength loss after strenuous resistance exercise. Larkin-Kaiser KA et al. 2015