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 studied intensively for a variety of ailments and conditions, from joint pain to wound healing, possibly because the cellular effects are theorised to 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, if any.
Light might interact with 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 the hypothesis is that both red and near-infrared light help our mitochondria to complete the process of respiration, giving more CO2 and ATP (energy). This would in theory apply 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 why light therapy researchers are interested in the application of targeting muscles, even more so than other tissues.
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 potential target of light therapy1,5, perhaps even 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 could be 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 the hypothesis behind light therapy is that it might be a potent promoter of mitochondrial function, a clear mechanism exists to explain how light could maybe improve our muscle growth and repair via stem cells.
Inflammation
Inflammation is a typical feature associated with muscle damage or stress. Some researchers think that light might help (if used appropriately) 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/fibrosis。