Jeremiah Ridderbos 12/28/2022
Low-Level Laser Therapy is more frequently used throughout rehab clinics and athletic settings than in the past. This review investigated the potential usefulness of low-level laser therapy (LLLT) for general populations and athletes by reviewing its efficacy on pain, recovery and performance. Eight clinical research articles were selected that related to the effect of LLLT on pain, recovery and performance. The majority of researchers on this topic conclude that LLLT to be effective in subjects with neck, back, joint and temporomandibular joint pain by causing an analgesic effect and increasing range of motion. It was also found that LLLT reduced delayed onset muscle soreness (DOMS) and upregulated protein synthesizing genes. Laser therapy was also found to improve muscular endurance and time to exhaustion. However, LLLT had no clear effect on muscular strength and performance. The results of the review indicate that photobiomodulation is beneficial for athletic and general populations pertaining to pain, recovery, aerobic and muscular endurance.
Keywords: Low-Level Laser Therapy, photobiomodulation, pain, muscular pain, recovery, muscular performance, endurance
Introduction
In today’s world musculoskeletal pain has become a large issue. It is estimated that 50 million U.S. adults suffer from chronic pain (Cheng et al., 2021). The problem of chronic pain also effects the entire economy. Chronic pain not only costs money to treat, it also costs money due to loss of productivity. Altogether, this cost astronomically adds up to $560-635 billion dollars annually (Cheng et al., 2021). Common pain relief methods include NSAIDs, serotonin-norepinephrine reuptake inhibitors, opioids, benzodiazepines and/or corticosteroids. However, these drugs include many undesirable side effects. Many individuals desperately looking for less destructive forms of pain relief.
One form of pain relief that is relatively new and still requires much research to find the full benefit is Low-Level Laser Therapy (LLLT). Low-Level Laser Therapy of photo biomodulation uses light to cause a variety of positive impacts for stressed or painful tissue. Some of the proclaimed effects of LLLT are reducing inflammation, boosting recover and healing, decreasing musculoskeletal pain and improving muscle strength and stamina.
Photobiomodulation works by variety of different mechanisms on a cellular level. Current research indicates that LLLT can decrease levels of pro-inflammatory cytokines that contribute to neuroinflammation and pain. This intervention was also found useful to increase anti-inflammatory and antioxidant activity and even activate peripheral opioid receptors (Matsuda et al., 2019). It has also been found that skin exposure to this type of therapy increases the amount of certain analgesic endorphins and serotonin. Both of these adaptions can suppress pain. In addition to this, photobiomodulation can stimulate vitamin D synthesis. Vitamin D has also been shown to decrease pain (by inhibiting certain prostaglandins) (de Sousa et al., 2018). Another way by which LLLT can alleviate pain and boost recovery is by activating parts of the mitochondria. Laser therapy has been shown to stimulate certain complexes of the mitochondrial respiratory chain and thus increase ATP production (Amaroli et al., 2021). These small changes at an intra-cellular level are thought to help the cell with a variety of functions such as replication, reparation, transporting nutrients and many other taxing cellular tasks. These tasks contribute to the muscles ability to recover and perform which directly impacts the daily activity of many populations.
This review will assess the degree to which LLLT induces adaptions in cellular function that translate to reducing pain, increasing performance and boosting recovery. This review will contribute to a better understanding of how useful photobiomodulation can be for the general population, athletes, and those experiencing chronic pain.
Synthesis of Literature
Methods
The articles were selected using the Boolean operators and key words photobiomodulation OR LLLT OR laser therapy AND pain AND muscular AND analgesic AND performance AND muscular strength AND muscular power AND recovery. These terms were used in a variety of combinations to find the most relevant articles related to the efficacy of Low-Level Laser Therapy in a sport setting and for the general population. The variables that were assessed in this data search was pain level, performance and recovery. Any article on light therapy that did not include a laser was not included in the review. No systematic reviews or meta-analysis were included. All articles were published within 10 years of the initial writing of the review.
Theme 1: Pain
One of the most well-known effects of photobiomodulation (PBMT) is pain relief. Pain relief is incredibly important today due to the astronomical numbers of injuries such as sprains, strains and a variety of back issues. These musculoskeletal (MSK) issues can be picked up through sports, occupation and activities of daily living. Photobiomodulation is known to increase microcirculation and decrease inflammatory cytokines and prostaglandin E2 (an inflammatory pain mediator). It is also thought to relax the muscle and stimulate tissue healing which is thought to alleviate pain to an extent. One randomized control trial investigated the effect of LLLT on individuals with myofascial neck pain. Laser therapy was applied on at least 8 areas, for times of 6 or 7 seconds. Both the placebo and treatment group were treated with the progressive release technique. While both groups significantly improved in symptoms, the group receiving laser therapy had a significantly more improved cervical range of motion and significantly less intense cervical pain compared with placebo. It was found that laser therapy significantly reduced pain in these subjects (Alayat et al., 2020). Another study done on individuals with chronic low back pain, found improved pain severity and range of motion following PBMT treatment five times a week for three weeks (Doğan, Ay, & Evcik, 2017). Even though there are varying results when it comes to LLLT and low back pain, there is great potential for LLLT to be a common treatment for low back pain. A study on individuals 8-16 years old, suffering from juvenile idiopathic arthritis shows that the analgesic benefits of PBMT reach beyond the muscle and tendons. After only 10, 8-minute daily sessions, the researchers found a significant drop in pain in the subjects over three time points in the LLLT group compared to the placebo group. While a greater range of motion and functional status was also observed, muscular strength remained the same (Elnagger et al., 2021).
Interestingly, temporomandibular joint (TMJ) pain is the third most common chronic pain that effects individuals (after spinal pain and tension headaches). A double-blind randomized control trial was done on 30 individuals with severe TMJ pain. The researchers applied laser to the area of concern three times a week for four weeks. The study included two laser groups and one placebo group. While pain slightly increased in the placebo group, it significantly improved in the laser group. Pressure pain threshold significantly increased with LLLT while the placebo group experienced no change. Pain intensity and range of motion were significantly improved in the laser group with no change in the placebo group (Sancakli et al., 2015). PBMT should be further researched for its high potential in analgesia.
Overall, these results show the extremely positive effect laser therapy has on pain. For individuals suffering from disorders such as arthritis or tendonitis, even small reduces in pain and dysfunction can make an incredible impact on daily activities. Research must continue on this cost-effective treatment in an effort to understand and apply it more effectively to populations in need.
Theme 2: Recovery
The ability to accelerate recovery is extremely valuable, not only to athletes but also to common individuals after procedures such as surgery, tendonitis or even wounds. While we will not look at the effect of LLLT on dermatologic conditions, this treatment has shown astounding impacts on muscular recovery. In the athletic setting, one significant limiter of exercise and an important recovery indicator is muscle soreness. This is sometimes referred to as delayed onset muscle soreness (DOMS). DOMS can severely limit the physical capability of individuals following intense exercise. Decreasing muscle soreness in individuals will allow for a quicker recovery, which allows people to get back to their daily activities sooner, whether its professional sports or hiking a trail. One way to do this is with Low-Level Laser Therapy. LLLT showed a significantly positive effect on calf muscle DOMS in a group of 16 college age individuals after a series of resistance, cardio and power exercises (D’amico et al., 2021). Another study done by Ferraresi et al. (2016) looked at DOMS, creatine kinase, mTOR and superoxide dismutase 2 (SOD2), which are biological markers associated with muscle damage, recovery and inflammation. This case study was done on two monozygotic twin college soccer which will eliminate any potential confounding variable related to genetic diversity in subjects. The study focused on muscle recovery, performance, hypertrophy and gene expression. While the variables related to performance will be addressed in a subsequent section, the remaining variables showed promising results for laser therapy. The results were measured following 12 weeks of intense resistance paired with laser therapy or a placebo laser. It was found that the individual receiving laser therapy had a significantly lower creatine kinase (CK) level in the blood which is indicative of muscle damage. The researchers also found SOD2 and mTOR gene expression to be increased when compared to the control. SOD2 is strongly associated with a better defense against oxidative stress while mTOR is known as an anabolic pathway that stimulates protein synthesis. It was also found that significantly more muscle hypertrophy had occurred in the individual treated with laser therapy when compared with placebo. This is in accordance with the elevated activation of mTOR gene expression leading to increased protein synthesis (Ferrareresi et al., 2016). Compared to a placebo, these results show significantly less intense post-exercise muscle soreness, less muscle damage, elevated protein synthesis and oxidation defense. Limitation of this study include a small sample size and a difference in RPE perception. All of these effects can help improve response to exercise by maximizing muscle size and minimizing long-term muscle damage. Increasing protein synthesis in response to exercise could be an effective way to stave off muscular atrophy in aging populations. This is one area that merits additional research.
Theme 3: Performance
Performance is the final aspect of photobiomodulation that will be covered in this review of literature. Many studies have looked at the effect of LLLT on performance in aerobic, muscular endurance, strength and power settings. Numerous studies have clearly shown that muscular endurance significantly improves with laser therapy treatment. Studies from Dutra et al. (2022), Farraresi et al. (2016) and Lanferdini et al. (2018) show increased muscular endurance and/or fatigue resistance when compared to control. These results clearly indicate that muscular endurance is positively impacted by this therapy. However, the results become unclear when it comes to strength and power. A double blind controlled clinical trial done by Maciel et al. (2014), shows a significant increase in torque generated by the LLLT group compared to the placebo in the second time window measured. However, no differences were observed between muscle recruitment or torque change. While another study found an improvement in time to exhaustion for every LLLT group included in competitive male cyclists, there was no increase in power output observed (Lanferdini et al., 2022). A previously referenced study done on two monozygotic twins showed no change in muscular strength, power or agility in the two groups (D’amico et al., 2021). On the other side of the spectrum, a study found photobiomodulation have positive effects on 1 repetition max leg press and leg extension when compared with placebo (Farraresi, 2016).
In view of these studies, there is little doubt that photobiomodulation can provide a significant benefit when it comes to lower intensity exercises targeting aerobic systems and muscular endurance. When it comes to strength and power, the evidence reviewed was heterogenous. This lack of compelling evidence for laser therapy benefiting anaerobic power can be explained by the proposed effect of photobiomodulation on cellular mechanisms. One of the major functions of photon energy in a cell is to activate cytochrome C oxidase, an electron transporter in the electron transport chain of the mitochondria. Activation of this compound is said to lead to increased ATP production within the mitochondria (Ferrareresi et al., 2016). During high intensity, low volume exercise, the body relies heavily on energy from the ATP-PCr system and anaerobic glycolysis. Neither of these metabolic pathways rely on oxygen and the electron transport chain to generate ATP. Contrarily, aerobic and endurance activities rely more heavily on ATP from the electron transport chain. This explains why LLLT had less of an effect on strength and power performance and a clear positive effect on aerobic and muscular performance.
Conclusion
The results of the studies analyzed showed that Low-Level Laser Therapy was effective in decreasing musculoskeletal pain and inflammation, improving muscular recovery and soreness, and in improving muscular endurance and time to exhaustion. The possibility for genetic variability causing any significant effect on pain, recovery or performance during the LLLT intervention has been nullified. There is strong evidence to supporting the use of PBMT for recovery and pain. While certain parts of performance appear to be positively affected by PBMT, the anaerobic aspects such as single and multi-leg strength and power have significant heterogenous results.
The findings of this review have impactful implications for both the general and athletic populations. With its effect on both musculoskeletal and joint pain it can be an extremely useful tool. LLLT has been shown to have analgesic effects on low back, which currently effects a significant proportion of the population. In addition to low back pain, this treatment has alleviated joint pain. A high number of athletes who suffer from joint pain could potentially utilize this technology to decrease pain and increase physical ability.
When it comes to recovery, PBMT is often used for the healing of incisions. However, the scope of its benefits in recovery is likely to be larger than many assume. Muscle building (via mTOR) is essential to both the general population and athletes. Many athletes are also limited by muscle soreness. PBMT has been shown to diminish DOMS which allows individuals to get back to their daily activities sooner and with more intensity.
Aerobic endurance is incredibly important not only for athletes, but also for the general population. For many untrained individuals who have difficulties walking extended distances, PBMT could be considered along with obvious lifestyle modifications such as exercise. When it comes to strength and power athletes, the evidence is still not clear on the effectiveness of PBMT. However, laser therapy would certainly do no harm, due to the fact that no adverse effects have been found.
Limitations
Across all aspects of laser therapy in this review, the doses applied varied. Laser wavelength, power output and energy density were not controlled across any of the studies. For example, when looking at laser power output, most studies used power outputs ranging from 7J/cm2 to 75J/cm2. However, certain studies used dosages much higher, even up to 405J/cm2. In addition to the lack of control in light intensity, the time of exposure varied significantly. When looking at certain effects of LLLT on human physiology, this inconsistency could be a confounding factor.
Future Research
While this review has shown LLLT to be effective for pain relief, recovery, aerobic training and muscular endurance, there is still not a clear consensus when it comes to strength and power. More research is required to sort out the currently heterogenous findings when it comes to strength and power. Studies looking at different power settings, wavelengths and exposure times of LLLT and its effect on strength and power exercises would be very beneficial. Additionally, research should also be conducted to find the correct intensity and duration of laser therapy for optimal pain relief and recovery. Exposing individuals to different wavelengths and exposure times will let practitioners know what the best time and intensity is for a specific condition. While this review did not investigate this question, the research is ambiguous when it comes to the type of laser, duration and intensity of exposure.
References
Alayat, M. S., Battecha, K. H., ELsodany, A. M., & Ali, M. I. (2020). Pulsed ND:YAG laser combined with progressive pressure release in the treatment of cervical myofascial pain syndrome: A randomized control trial. Journal of Physical Therapy Science, 32(7), 422–427. https://doi.org/10.1589/jpts.32.422
Amaroli, A., Pasquale, C., Zekiy, A., Utyuzh, A., Benedicenti, S., Signore, A., & Ravera, S. (2021). Photobiomodulation and oxidative stress: 980 nm diode laser light regulates mitochondrial activity and reactive oxygen species production. Oxidative Medicine and Cellular Longevity, 2021. https://doi.org/10.1155/2021/6626286
Cheng, K., Martin, L. F., Slepian, M. J., Patwardhan, A. M., & Ibrahim, M. M. (2021). Mechanisms and pathways of pain photobiomodulation: A narrative review. The Journal of Pain, 22(7), 763-777.https://doi.org/10.1016/j.jpain.2021.02.005
D’Amico, A., Silva, K., Rubero, A., Dion, S., Gillis, J., & Gallo, J. (2022). The Influence of phototherapy on recovery from exercise-induced muscle damage. International Journal of Sports Physical Therapy, 17(4), 658–668. doi:10.26603/001c.34422
de Sousa, M. V. P., Kawakubo, M., Ferraresi, C., Kaippert, B., Yoshimura, E. M., & Hamblin, M. R. (2018). Pain management using photobiomodulation: Mechanisms, location, and repeatability quantified by pain threshold and neural biomarkers in mice. Journal of Biophotonics, 11(7), Article e201700370. https://doi.org/10.1002/jbio.201700370
Doğan, S. K., Ay, S., & Evcik, D. (2017). The effects of two different low level laser therapies in the treatment of patients with chronic low back pain: A double-blinded randomized clinical trial. Journal of Back & Musculoskeletal Rehabilitation, 30(2), 235–240. https://doi.org/10.3233/BMR-160739
dos Santos Maciel, T., Muñoz, I. S. S., Nicolau, R. A., Nogueira, D. V., Hauck, L. A., Osório, R. A. L., & de Paula Júnior, A. R. (2014). Phototherapy effect on the muscular activity of regular physical activity practitioners. Lasers in Medical Science, 29(3), 1145–1152. https://doi.org/10.1007/s10103-013-1481-4
Dutra, Y. M., Malta, E. S., Elias, A. S., Broatch, J. R., & Zagatto, A. M. (2022). Deconstructing the ergogenic effects of photobiomodulation: A systematic review and meta-analysis of its efficacy in improving mode-specific exercise performance in humans. Sports Medicine, 52(11), 2733–2757. https://doi.org/10.1007/s40279-022-01714-y
Elnaggar, R. K., Mahmoud, W. S., Abdelbasset, W. K., Alqahtani, B. A., Alrawaili, S. M., & Elfakharany, M. S. (2021). Low-energy laser therapy application on knee joints as an auxiliary treatment in patients with polyarticular juvenile idiopathic arthritis: A dual-arm randomized clinical trial. Lasers in Medical Science, 37, 1737–1746. https://doi.org/10.1007/s10103-021-03427-6
Ferraresi, C. , Bertucci, D. , Schiavinato, J. , Reiff, R. , Araújo, A. , Panepucci, R. , Matheucci, E. , Cunha, A. F. , Arakelian, V. M. , Hamblin, M. R. , Parizotto, N. & Bagnato, V. (2016). Effects of light-emitting diode therapy on muscle hypertrophy, gene expression, performance, damage, and delayed-onset muscle soreness: Case-controlled study with a pair of identical twins. American Journal of Physical Medicine & Rehabilitation, 95(10), 746-757. https://doi.org10.1097/PHM.0000000000000490.
Lanferdini, F. J., Bini, R. R., Baroni, B. M., Klein, K. D., Carpes, F. P., & Vaz, M. A. (2018). Improvement of performance and reduction of fatigue with low-level laser therapy in competitive cyclists. International Journal of Sports Physiology & Performance, 13(1), 14–22. https://doi.org/10.1123/ijspp.2016-0187
Matsuda, M., Huh, Y., & Ji, R.-R. (2019). Roles of inflammation, neurogenic inflammation, and neuroinflammation in pain. Journal of Anesthesia, 33(1), 131–139. https://doi.org/10.1007/s00540-018-2579-4
Sancakli, E., Gokcen-Rohlig, B., Balik, A., Ongul, D., Kipirdi, S., & Keskin, H. (2015). Early results of low-level laser application for masticatory muscle pain: A double-blind randomized clinical study. BMC ORAL HEALTH, 15, Article 131. https://doi.org/10.1186/s12903-015-0116-5
Journal Review 