# Effects of Photobiomodulation in Sports Performance: A Literature Review
## 1 Introduction  
Photobiomodulation (PBM) is a non-thermal treatment that uses sources of non-ionizing light, such as light-emitting diodes (LEDs), lasers and broad spectrum light in the visible to infrared portion of the spectrum. The use of PBM triggers reactions photophysically and photochemically in various tissues in the human body by interacting with chromophores [1]. The photoreceptors in the mitochondria are stimulated by light, which can trigger a stimulation or, contrarily, an inhibition of the cellular metabolism. The optimal doses are those that trigger therapeutic effects [2, 3, 4]. The PBM mechanism of action involves bioenergy, photochemistry and photobiology. Transcription factors and signaling pathways are activated when photons are absorbed by certain molecules within the neurons and the metabolic reaction speeds in the cells are changed. Additionally, the absorption of photons increases oxygen consumption which leads to greater activity in the mitochondria and oxidative phosphorylation. Therefore, there is additional adenosine triphosphate (ATP) manufactured, providing more energy for transduction in the neurons. The function of the brain is thus improved as blood flow to the brain is increased [2]. Within the realm of the possible therapeutic benefits of photobiomodulation, its effect on mitochondrial function is the best researched. In this regard, the mitochondrial electron transport chain complexes I, II, III and IV and succinate dehydrogenase have beenshown to increase their activity. A greater level of ATP is seen through an increase in transmembrane protein complex IV, commonly referred to as the enzyme cytochrome C oxidase. Additionally, PBM activates transcription factors and signaling pathways which results in a greater gene expression related to the synthesis of proteins, migration and proliferation of cells, anti-inflammatory responses, antioxidant enzymes and antiapoptotic proteins [3]. Photobiomodulation therapy is commonly used in clinical practice to treat musculoskeletal disorders, with positive results shown in various clinical trials and systematic reviews [4]. However, widespread use of and strong scientific interest in the effects produced after the application of PBM in the field of sports performance also occur. The affirmative benefits of photobiomodulation on biological markers which relate to the reduction of oxidative stress, the modulation of inflammation and the damage to muscles have been shown in various studies [1]. [PERSON] et al. evaluated how peripheral blood cells, namely granulocytes, lymphocytes and erythrocytes, have their oxidative metabolism affected by the action of PBM. Samples of heparinized blood from fifteen participants were irradiated, with the results showing an increase in both the oxygen saturation and the partial pressure. Hence, the reactions induced photochemically in the aforementioned cells by PBM can improve the oxygen carrying capacity of the blood [5]. After strenuous exercise, elite athletes frequently suffer from muscle fatigue which is usually linked to oxidative muscle stress from the increased production of reactive oxygen species. This provokes a physical performance reduction and, possibly, injuries, hence the fastest and most effective healing treatment for the athlete is essential [6]. In sports performance, it was shown that the use of PBM before physical training could improve sports performance in top-grade athletes in addition to reducing the delay in muscle fatigue and preventing the anticipated rise in the level of blood lactate [5]. Participants, in a good state of health, and professional sports players have shown in various clinical research programs that when PBM is used before a training session the number of repetitions performed can be increased, the time to fatigue onset can be lengthened and the peak torque can be improved. Additionally, studies demonstrated that PBM can enhance gains in different areas of physical training abilities such as strength and cardiovascular training [5].