The number of sports-related injuries is on the rise every year. Each year in the United States, an estimated 30 million children and adolescents participate in organized sports [1] and approximately 150 million adults participate in some type of nonwork-related physical activity [2]. While engaging in these activities has numerous health benefits it also involves a risk for injury. According to the Centers for Disease Control's (CDC) analyzed data from the National Electronic Injury Surveillance System All Injury Program (NEISS-AIP), the most common injuries reported after participation in sports-related activities include damage to the skin and subcutaneous tissue, sprains and strains to muscle, ligaments, tendons, and bone in the upper and the lower limbs, trauma to the spine, and soft tissue edema [3]. Phototherapy has been used for the treatment of many chronic problems, such as tendinitis, capsuilitis, temporomandibular joint problems, muscle pain [4, 5]. However, similar injuries are also reported after participation in a sport or recreational activity. The addition of the co adjuvant light therapy can accelerate wound healing and decrease inflammation.

Light emitting diodes were originally manufactured for their use in electronic and laboratory equipment, and contained a silicon carbide (SiC) semiconductor. Today, such devices have expanded to use in medical applications, such as those used in wound healing, inflammation reduction and pain management, but instead use gallium arsenide phosphate (GaAsPa) as a semiconductor. Light emitting diodes Gallium arsenide phosphate (GaAsPa) possess a direct band gap, unlike silicon carbide (SiC), allowing it to absorb and emit light more efficiently producing near infrared (red), near infraorange (orange), and near infrayellow (yellow) color light [6]. Near infrared (red) light has the deepest penetration. In light emitting diodes, gallium arsenide phosphate (GaAsPa), used to emit red and infrared light, will be discussed in this paper [7].

Near infrared light therapy, also known as phototherapy is a process that explains the biochemical responses that tissues exhibit when exposed to light energy from sources such as lasers, light emitting diodes, and fluorescent lamps. During medical treatment near infrared gallium arsenide phosphate devices used for light emitting diodes (near infrared and gallium arsenide phosphate) are applied to the site of injury or pain, allowing light to directly penetrate the tissue. [8] Despite complete understandings of the physiology and biochemistry involved, light has been used on humans and other organisms for centuries in response to its positive effects. More recently, studies found during this review attempted to discover the wavelengths in which most optimal results are produced, using light emitting diodes that operate within wavelength ranges of 630-1000nm. Results tended to be positive at various wavelengths, implicating that the light produced by near infrared light emitting diodes itself is a beneficial aid in healing. This article will specifically address the medical near infrared light emitting-diode, a monochromatic, non-coherent, solid state semi-conductor diode that emits light in the near infrared range when a current is applied through the device.

In contact sports, such as American football/rugby, 51% of the 1.2 million participants received injuries during the training year, with an increasing number of brain concussions [9, 10]. Soccer players with skin and soft tissue injury (edema) frequently experience ankle sprains, Achilles tendonitis, lumbar femoral fractures, hamstring tears and strains, muscle cramps or ruptures, blisters, knee injuries such as anterior cruciate ligament (ACL) tears, shin splints, pulled or strained calf muscles, cervical discs, and concussions due to the extreme nature of the sport [11, 12]. Hockey players sometimes experience concussions (due to unexpected violence from players and/or spectators), face and dental injuries, cuts, lacerations, bruises, muscle cramps, clavicle fractures, shoulder separation, ankle sprains, finger fractures and, herniated disks [13, 14]. For basketball players, of 3843 injuries examined, 13.2% were lateral ankle sprains,11.9% showed patellofemoral inflammation, 7.9% lumbar strains, and 3.3% demonstrated hamstring strains. (American Academy of Orthopedic Surgeons-AAOS; 2006 U.S. Consumer Product Safety Commission’s National Electronic Injury Surveillance System-NEISS) [15, 16]. Boxing injuries include cuts and bruises, sprains and strains to the ankle and wrist, concussions (memory, Parkinson’s, and dementia), fractures (eyes, nose, hand, jaw, and ribs), shoulder discoloration, and tendonitis or ligament injury [17]. Wrestling /Sumo wrestling also results in a high number of injuries due to the aggressive nature of the sport as well as Polo players possibly having a higher number of concussive and body injuries [18-20].

Injuries also prove to be frequent in noncontact sports such as swimming, rowing, golf, baseball, skiing, gymnastics, biking, and table tennis. Among the most common area of injuries in such sports are lower back, knee joint, wrist (carpal/ulna ligament tendonitis), shoulder rotator, ligaments, ankle joints, as well as fractures of the upper and lower limbs and facial injuries. Brain concussions can also happen, especially in baseball catchers [21-26]. Muscle strains on the hand, wrist, elbow, and lower limbs are more susceptible to chronic tendonitis due to chronic overuse and repetition of injury.

Most common soft tissue traumas of the shoulder are due to frequent use of the arms above the horizontal plane. Typically, these traumas are developed in throwing or racquet sports (such as tennis, baseball, javelin, pole vaulting), but golfers, swimmers, and weight lifters are also susceptible [27-29].

Elbow injuries result directly from chronic repetitive forces that occur during the act of throwing and are traceable directly to the mechanism of throwing [22]. Other injuries typical to the racquet sports are injuries where the participant develops elbow pain secondary to force overload or improper technique. Notably, 21% of all overuse injuries involve the elbow [30].

The wrist is a complex joint capable of motion in three planes. The wrist can sustain injury in a wide variety of sports and recreational activities in which weight bearing, twisting, throwing, and impact occur [31].

General mechanisms of hip injuries are the result of direct acute trauma (contact/collision sports) or overuse (noncontact or endurance sports). The majority of knee injuries fall into the overuse categories of; tendonitis (20%), apophysitis (10%), and chondropathy (10%) [32]. Lateral compartment ligament sprains of the foot involve inversion+planatar flexion+adduction injury. Medial compartment ligament sprains involve eversion, dorsiflexion, and adduction. Achilles tendinitis (frequent in soccer players and hamstring injuries of baseball pitchers) involves repetitive overloads, particularly with faulty technique or association with weakness and inflexibility of the gastrocsoleus complex [33].

All types of sports have a potential for injury, whether from the trauma of contact with other players or from overuse or misuse of the specific body part. With all the injuries stated above the use of the light emitting diode gallium arsenide phosphate (red light) can be used as an immediate therapy which still going to a medical professional for treatment. Until further research has been conducted any near infrared light emitting diode therapy should never be used on the retina, pregnant women, children, or oncological patients as there is not sufficient research to prove its safety in these areas.

Mitochondria are thought to be a likely site for initial effects of near infrared light, leading to increased adenosine triphosphate (ATP) production resulting in increased cellular oxygenation [35, 36]. Stimulated adenosine triphosphate (ATP) is an immediate energy source for muscle contraction, stimulated vascular endothelium and fibroblast growth factor and an increase in new capillary cellular migration in the metabolism of all cellular repair processes [37, 38]. These effects in turn lead to increases in vascular endothelium growth factor will produce new blood capillary formation activity by promoting improvement in the metabolism of protein production, calcium, zinc, phosporylation, dismutation, and the cycchrome c oxidase cascade effect. It also provides improvement in the metabolism of nitric oxide [39], increases in cellular proliferation and cellular polynuclear migration stimulating fibroblast activity and microphages and microglia migration [40]. As proposed by Poyton and Ball, cytochrome C oxidase functions in photobimodulation are created by producing nitric oxide, a signaling molecule which can then function in both intra- and extracellular signaling pathways [41]. The results of these biochemical and cellular changes include such benefits as increased healing in chronic wounds, improvements in sports injuries, reduced pain and inflammation, and lessened peripheral nerve damage [42].

When applied at the early stage of wound repair, near-infrared light-emitting diodes are able to completely reverse the detrimental effects of tetrodotoxin. This occurs via the mechanism of photobiomodulation that involves the up-regulation of cytochrome c oxidase, leading to increased metabolism in neurons functionally inactivated by toxins [43]. Near-infrared light-emitting diode-induced therapy generated increases in Nitric Oxide, Adenosine tri-phosphate, and neurotransmitters, vascular endothelium, tumor necrotic, insulin, and epidemis growth factors, and gene transition that resulted in stimulating higher activity in cell proliferation and differentiation into mature cells [44, 45]. Increased numbers of myofibroblasts, myofibrils, and myotubules have also been clinically documented after light therapy [46]. Additionally, satellite cells, the precursor cells in the process of muscle regeneration, also show an increase in proliferation when irradiated with near infrared light therapy [46].

In a small study conducted by Min, et al. human wounds were treated with multiple sessions of near infrared light therapy using 830 nm, continuous wave, irradiance of 100mW/cm(2). It was concluded that the light emitting diode gallium arsenide successfully brought about accelerated healing in wounds of different etiologies and at different stages, and successfully controlled secondary infections [48]. Spitler, et al. concluded that low level laser and near infrared light emitting diode gallium arsenide induced comparable levels of cell migration and wound closure [49]. Macrophages are a source of many important mediators of wound repair. Young, et al. suggested that light at certain wavelengths may be a useful therapeutic agent by providing a means of either stimulating or inhibiting fibroblast proliferation where necessary [50].

Overall, the use of near infrared light therapy reduced healing time when used from the time of injury onset through to a mature healed wound. It is important to start the near infrared light therapy immediately in the sport arena and to continue the application two to three times a day, for ten to fifteen minutes to accelerate the physiopathology of wound healing. The primary points of interest on wound healing with the use of near infrared light include the status of tissue perfusion, the role of bacterial contamination, pressure applied to the tissue, and the immune status of the host [51].

A number of clinical studies have also demonstrated the efficacy of infrared light on acute and recalcitrant wounds. In sports like hockey, boxing, wrestling that may involve facial, oral, and/ or dental injuries; there have been studies that show a positive-tissue response through stimulation of osteoblasts and a decrease in the swelling of the gum and with tooth distractions [52]. Faria, et al. evaluated the effects of photosensitive drugs activated through a near infrared light emitting diode using the eight mongrel dog osseointegration processes. The results demonstrated a tendency to stimulate bone formation similar to an autogenous bone graft on a later point of recovery [53]. Pagin, et al. found similar effects on the stimulation of cell growth, but no effect on cell differentiation [54].

In a double-blind study of recalcitrant venous stasis ulcers in non-diabetic patients, all subjects who received an active infrared treatment either healed completely or demonstrated significant reductions in the wound area during the next two to six months in contrast to untreated patients [55]. Using near infrared molecular spectroscopy, the diabetic ulcer are observed to have low levels of oxygen. With the treatment of near infrared light healing is accelerated; most likely due to the stimulation of the mitochondria, adenosine triphosphate, adenosine diphosphate, and the improved oxygenation of the cells. The total collagen content was significantly increased at two months when compared with control groups. The beneficial effects of near infrared light on wound healing can be explained by considering several basic biological mechanisms including the induction of expression cytokines and growth factors known to be responsible for many phases of wound healing [56]. The near infrared light emitting-diode phototherapy system has the correct wavelength for the target cells, delivers an appropriate power density and an adequate energy density [57]. Whelan, et al. stated that the use of NASA light-emitting diodes for light therapy could greatly enhance the natural wound healing process, and could allow the patient to return more quickly to a preinjury/illness level of activity [58].

Inflammation is the tissue’s response to injury, no matter what the cause or type. Inflammation can generally be categorized as mild, moderate or major. Mild tissue inflammation or delayed onset muscle soreness (DOMS) is experienced one-two hours after activity and may be experienced by individuals who have been physically inactive for prolonged periods of time, and begin a dynamic (to them) bout of exercise. It also can occur in athletes who exercise beyond their normal limits of training. Moderate tissue inflammations have a history of two-three weeks of long standing pain late in the activity or immediately after vigorous activity. Major tissue inflammation, and/or bone or tendon microtrauma have a history of three-four weeks of pain in the early or middle stages of activity. Patients will demonstrate point tenderness, heat, erythema, swelling, and/or crepitation. Therapeutic effects of near infrared light emitting-diodes have been shown to reduce inflammation and swelling in chronic conditions of arthritis, bursitis, tendonitis, and pain control. In an experiment conducted by Xavier, et al.fifty-six male Wistar rats were divided into groups; control, Achilles tendonitis group, and near infrared light emitting diode group. Therapy was initiated 12 hours after the Achilles tendinitis induction (injection catalyst to produce tendinitis), with a 48-hour interval between irradiations. The histological analysis and inflammatory mediators were quantified. Their results suggest that the anti-inflammatory therapy with early application of a near infrared light emitting-diode (880nm) was able to reduce signs of inflammation in collagenase-induced tendinitis by reducing the number of inflammatory cells and decreasing mRNA expression of cytokines [72]. Increased activity of the mitochondria, ADP (adenosine diphosphate) and ATP (adenosine triphosphate), removal of the free radicals and decrease of the (tumor necrotic and interleukin-6) growth factors can produce better atrophic cellular healing thereby accelerating the recovery of injured tissue.

Sports induced traumatic brain injuries have received increased attention over the last decade in the medical literature, catastrophic injuries, sports competition, and in social media [76]. As previously mentioned, concussions in the adult athlete are increasingly recognized injuries that occur in American football, volleyball, basketball, wrestling, baseball, bicycling, softball, skiing, hockey and boxing. Traumatic brain injuries are challenging given the elusiveness of the injury, the sensitivity and specificity of the evolving nature of concussive injury, cognitive dysfunction, post traumatic stress syndrome (PTSD), and chronic traumatic encephalopathy following repetitive injuries [77]. Repeated mild traumatic brain injuries occurring over an extended period of time may result in cumulative neurological and cognitive deficits. Retired American professional football players with a history of three or more concussion injuries were five times more likely to have mild cognitive impairment, intracranial bleeding, and brain edema. Later they may have multiple scar tissues, which could lead to memory loss, Parkinson’s and Alzheimer’s disease, depression, and abnormal behavior [78]. Professional boxers are also well known to have a risk of significant cognitive decline and alterations in brain functions [79, 80].

Oron, et al. they assessed the possibility of various near-infrared light therapies on mice producing a beneficial effect on the long term neurobehavioral outcomes and brain edema; this was confirmed using magnetic resonance imaging [81]. Quirk, et al. showed statistically significant preclinical outcomes that support the use of near infrared light treatment after traumatic brain injury in effecting changes at the behavioral, cognitive, cellular, and chemical levels [82].

Emerging technologies and novel approaches that aid in sports concussion diagnosis and management are being introduced at a rapid rate. The use of near infrared oxygen spectroscopy provides a significant tool of diagnosis of the cerebral oxygenation [83]. Production of low levels of reactive oxygen species, modulated expression of 111 genes in the cDNA microarray study, and increased nerve cell proliferation and migration. This may provide a significant functional benefit with an underlying mechanism of possibly being induction of neurogenesis [84-90].

In initial experiments performed by Khuman, et al. where low level light therapy of 780nm was administered transcrainially to mice may prove to be a good therapeutic option to improve cognitive recovery. Results were found to limit (reduce) brain edema future consciousness after traumatic brain injury [91]. In a case study of two human chronic traumatic brain injury cases using 800nm therapy, cognition improved following treatment with red and near infrared light emitting-diodes. Although the treatment of chronic and traumatic brain injury is promising, patients still showed regress with non-treatment of near infrared light emitting diodes after more than two weeks. Transcranial light emitting-diode could improve cognition, reduce costs in traumatic brain injury treatment, and may be applied at home or any other home care facility [92]. In two separate case studies, Naesser, et al. and Quirk, et al. both showed significant support for the use of near-infrared treatment after traumatic brain injury in effecting changes at the behavioral, cellular, and chemical levels. Participants and their family members reported improved sleep and better ability to perform social, interpersonal and occupational functions [76, 94]. While some technologies show promise, their clinical utility remains to be established. There is a need for more randomized double- blind research along these lines for the future of human studies.

Spinal cord injuries with catastrophic outcomes can occur in a variety of sports, both contact sports such as American football, wrestling, soccer, and riding accidents (equestrians) and non-contact sports such as skiing, gymnastics, and diving [95]. According to Okada, the pathophysiology of spinal cord injury it is a two-step process; early spinal shock mechanical injury followed by secondary auto-destructive injury. Mechanical trauma leads to disruption of the spinal blood barrier, neural cell death, axonal damage, and demyelization. This phase is followed by the secondary injury that expands the additional inflammatory reaction at the lesion site with neurotransmitters, interleukin (IL)-6, vascular endothelium, and human neurotrophic growth factors. Microglias, immune cells in the central nervous system have been reported to proliferate and become activated in the damage neuronal tissue. Activated microglia release many substances. These contribute to degeneration and regeneration after spinal cord injury. However, it is unclear if they directly induce damage of neurons and oligodendrocytes. On the other hand, activated microglia shows a neuroprotective effect in the production of neurotrophic factors. It is necessary to develop an effective treatment to inhibit secondary neuronal damage and to promote neuronal regeneration after spinal cord injury. Currently suppression of the secondary neurodegeneration has been performed with the use of high doses of steroids. The possibility of introducing near infrared light emitting diode immediately after injury would inhibit glial destruction and scaring and gradual functional improvements of injured tissue [8]. However, according to Jagdeo, et al. 2012 a question is raised as to the depth of penetration (4cm) of near infrared light emitting diode in cadavers [96]. According to a comparative study by Giacci, et al. it will be necessary to optimize delivery devices, wavelength, intensity and duration of red, near infrared irradiation therapy individually for different central nervous system injury types [97]. In the study conducted by Wu, et al. results suggest that near infrared light therapy applied non-invasively promotes axonal regeneration and functional recovery in acute spinal cord injuries caused by different types of trauma. These results suggest that light is a promising therapy for human spinal cord injuries [98]. In an experiement conducted by Paula, et al. using thirty-one Wistar rats, the objective of the study was to investigate the effect of low level laser therapy on the locomotor functional recovery, histomorphometric, and histopathological changes of the spinal cord after moderate traumatic injury in the rats. The results showed faster motor evolution in the rats with spinal contusion treated with low level laser therapy, preservation of nerve tissue in the lesion area, inflammation control and an increase in the number of nerve cells and connections [99].

Sports-related injuries commonly involve the musculoskeletal system. However, peripheral nerve lesions are more serious and may delay or preclude the athletes’ return to sports. In multiple studies by a number of different authors all doing some form of peripheral nerve dissection, all are finding similar positive influence on the acceleration of the functional nerve recovery using rat injury models [100, 101]. Examples of sports related nerve entrapment syndrome can be seen in biking with handlebar palsy; intrinsic ulnar compression of the deep terminal motor branch of the ulnar and medial nerve as well as in subclavian and vertebral arteries following blunt force trauma all of which occur in sports [102]. The use of new therapeutic approaches for peripheral nervous system repair is currently being investigated in an attempt to achieve early functional recovery. In an experiment performed by Mohammed, et al. using 901nm using on twenty- four New Zealand adult male rabbits affirms the beneficial effects of near infrared light on nerve regeneration. The results produced a significant amount of structural and cellular change, suggesting that photomodulation by the light in the near-infrared range can accelerate nerve repair and may be a viable approach for nerve regeneration [103].

Preservation of the biochemical processes in muscles is a major challenge in patients with severe peripheral nerve injury. In a double-blind, placebo-controlled study by Rochkind, et al. 2009 and 2013, patients with incomplete long term peripheral nerve injury, using low level laser therapy of 780nm irradiation progressively improved peripheral nerve function. This can lead to significant functional recovery and could have a direct therapeutic application on muscle recovery, especially during progressive atrophy resulting from peripheral nerve injury [103, 104].

Post traumatic nerve repair and prevention of muscle atrophy represent a major challenge for restorative medicine. In another double-blind randomized study, Shamir, et al., showed that postoperative near infrared irradiation enhances the regenerative process of peripheral nerves after complete transection and anastomosis through a rat sciatic nerve [106, 107]. This suggests that patients with peripheral nerve injury can progressively improve nerve motor function, which again would lead to significant functional recovery [108]. In a double-blind study conducted by Rochkind, et al. suggested that postoperative 780nm laser phototherapy enhances the regenerative process of the peripheral nerve [109, 110]. Gomes, et al. also concluded that the use of low-level laser therapy showed significant increase in neurotrophic factor expressions and inflammatory process reduction, an important aid to the nerve regeneration process [111].

In a 2005 study by Vinck, et al. a near infrared light emitting diode was used in place of low-level laser therapy to see the potential explanatory mechanisms of peripheral neurophysiology in vivo. Based on the results, they concluded that near infrared light emitting diode irradiation produced an immediate and localized effect upon conduction characteristics in underlying nerves. Moreover, the outcome of the study yielded a potential explanation for pain relief induced by near infrared light emitting diodes [112]. Many racquet sports players and even golfers have elbow and wrist injuries. In a controlled study by Naeser, et al. they applied near infrared light therapy to acupuncture points to see if it significantly reduced pain in carpal tunnel syndrome, the results were that patients could perform previous work (computer, typists, and handyman) and were stable for 1 to 3 years [113].

The treatment of injury and pain has a long history and covers such topical remedies as ice baths, heat, massage, and acupuncture [114]. Medicine sought the advantage of medical properties of a variety of plants containing natural opiate substances, acetylsalicylate, NSAID (Non-Steroidal Anti-Inflammatory), and psychotropic drugs. This led to a focus on the pharmaceutical treatment of pain, almost to the exclusion of non-pharmaceutical approaches. But drug therapy comes at a price. The side effects such as gastrointestinal bleeding/risks, safety, efficacy, and the potential for addiction and abuse are just some of the problems associated with these pharmaceutical approaches [115]. On a positive note, these issues have contributed to the search for complementary medicine for pain and healing. Lim, et al. suggests that 635 nm irradiation inhibits prostaglandin E (2) (PGE(2)) synthesis like cyclooxygenase (COX) inhibitor and appears to be a useful as an anti-inflammatory tool [116].

Near infrared light emitting diode therapy has been known as a phototherapy since its discovery using Einstein’s electromagnetic wave theory [57]. Near infrared therapy has been obtained using low level laser however, using lasers to produce such therapy have their disadvantages; they need large spaces to house equipment, are difficult to use, require training of the personal for use, and are very expensive. Monochromatic noncoherrent near infrared light emitting diode on the other hand can be portable, are more economically accessible, and can be used in any location with battery operated equipment.

The introduction of the light emitting diode by NASA, to produce near infrared invisible light has been proven to be an acceptable form of therapy in the medical community. The Food and Drug Administration (FDA) has recently cleared multiple near infrared light emitting diode gallium arsenide 640nm to 940nm devices for the treatment of a variety of medical conditions. In 2000 at the Sydney Olympics, the U.S. Olympic training facilities released statements of endorsement for their athletes using the light emitting-diodes gallium arsenide [57]. Enwemeka, et al. have shown that the near infrared light emitting diode has a cumulative healing effect and is often used in sports medicine for muscle pain [117].

Physiotherapists’ and sports medicine specialists are treating a wide variety of acute and chronic musculoskeletal injuries and pain with phototherapy. The benefit of light therapy reduces the discomfort of pain and inflammation while promoting blood flow and the body’s own tissue repair mechanism [118]. Particular advantages of using the near infrared light emitting diode as opposed to other forms of invasive therapies are rapid patient response which reduces injury recovery time, operator and cost effectiveness, and suitability for home treatments, professional and non-professional facilities.

According to Kim, et al. clinical and experimental evidence support the use of near infrared light emitting diode as an adjunct in treating in the medical field [119]. Recently, near infrared light emitting diodes have been used for muscle fatigue and recovery. In a double-blind randomized placebo-controlled trial using eighty-six human patients for nonspecific knee pain, Leal-Junior, et al., concluded that near infrared light emitting diode is effective in decreasing pain and improving the quality of life for patients [75].

Near infrared light emitting diodes can provide an immediate therapy after an injury occurs. It is a safer and more affordable technology for delivering phototherapy. By covering a broader surface but in a narrow and more concentrated portion of the light spectrum treatments, it can be more effective than a traditional low level laser application for which a subject must be transported; a patient can be treated immediately by a near infrared light emitting diode which generates less heat reducing the secondary tissue damage. The ever-shrinking size of the units and the ability to be used in clinical and non-clinical settings makes the near infrared light emitting diode very attractive to clinicians, physical therapists, and patients for soft tissue procedures. It has been proven to be an adjuvant therapy and may offer profound impact for the treatment of wound healing, pain, and musculoskeletal injuries. New and ongoing clinical research including additional clinical applications, and more randomized double-blind analysis on a larger scale, should be encouraged for individuals who have experienced chronic, acute injuries and/ or sports-related injuries. More evidence-based research should be conducted to develop this growing field for even greater application.

The authors wish to thank Beth Konikoff for editing.

The authors declares that there is no conflict of interest regarding the publication of this paper, nor received any financial compensation or other consideration in connection with the preparation and/or publication of the this manuscript.

Dr. Manuel Dujovny, Wayne State University School of Medicine, and Dr. Keith M. Tobin, Livonia, Michigan recommend publication of this article.