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Sport Sciences
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.
- photobiomodulation
- sport
- exercise
- endurance
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 been shown 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].
Wasik 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]. However, the specific effects that PBM produces in athletes and which benefits it can bring to different sports need to be clarified. The latest summary of research shows that the best effects of PBM therapy occur when the light is used before the exercise in direct contact with the skin using wavelengths from 655 to 950 nm. Furthermore, the majority of positive results happened with an energy dose ranging from 20 to 60 J for small muscular groups and 60 to 300 J for large muscular groups and maximal power output of 200 mW per diode [6,7,8,9].
2. Cardiovascular Training
In five out of the eight studies in which the intervention is cardiovascular training, an increase in running performance in the group that received PBMT before the test is observed. This increase is due to better oxygen consumption which leads to a delay in time to exhaustion [1,12,16,20,22]. In one of the studies, there was a moderate change in pain reduction after a 5km run in the group that had received PBMT compared to the placebo group [15].
In two studies, in which the therapy was applied 6.5 h before the test, no significant changes were found between groups. Consequently, the lack of results may be due to the time frame for the application of the therapy and the start of the protocol [13,21].
3. Strength Training
Of the five studies in which the intervention consisted of a strength test with concentric and eccentric exercises measured using an isokinetic dynamometer, four were found to show significant changes in the group in which PBMT was used compared to the placebo group. In three of them, muscle damage after exercise was reduced [11,18,19] and, in the other, fatigue and time to exhaustion were observed to decrease [14].
In the study in which no significant differences were found in muscle damage between the experimental and control groups, different PBMT parameters were observed to reduce fatigue. Hence, future studies need to clarify what the appropriate parameters are in order to increase the quality of PBMT [17].
4. Combined Cardiovascular and Strength Training
Among the two studies in which the intervention was a combination of cardiovascular and strength exercise tests, neither demonstrated the effectiveness of PBMT, applied before or after exercise, for muscle recovery in high-intensity cardiovascular exercise [6,18].
However, one of the studies showed that muscle recovery is greater after strength training in the group that received PBMT when compared to the placebo group [18].
5. Effects and Benefits of PBMT on Sports Performance
Studies show that PBMT helps improve sports performance and accelerates recovery after exercise, in both strength and cardiovascular training, so it is a technique that can be used in numerous sports disciplines [20].
6. Characteristics PBMT Must Have to Improve Sports Performance
There are still many open questions about the application of PBMT in sports, but from all the studies reviewed the best results regarding muscle damage are obtained with a dose of between 10 and 60 Joules, and for a greater effect the therapy should be performed before and after exercise [8].
7. Strengths and Weaknesses of the Study
Some strengths should be mentioned. Good methodological quality in the clinical trials was ensured by the use of scales. The randomized clinical trials that were collected were of high quality, and hence so were the results obtained.The demographic characteristics of the study samples were homogeneous (healthy people aged between 20 and 35 with no musculoskeletal injury at least three months prior to the intervention). However, some weaknesses must be acknowledged. There was a lack of scientific information on PBMT in sports. In some studies, the samples contained a low number of participants. The interventions in various studies were of short duration, with a low number of training sessions. The majority of the randomized clinical trial samples were healthy people but not top-level athletes, which could have interfered with the results.
8. Methodological Quality of the Obtained Results
The methodological quality of the studies was performed using two scales: the PEDro scale [10] and the IVS for randomized clinical trials.
9. Future Research
After analyzing the results, it is clear that there is a scarcity of scientific evidence on this subject. Consequently, different lines of research are proposed:
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Implementation of RCTs to clarify PBM parameters such as the analysis of the optimal wavelengths, the optimal times and whether therapy should be performed before or after exercise.
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Implementation of RCT with samples from top-level athletes to see if there are differences from healthy untrained people.
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The evaluated PBM effects are combined with the effects of physical activity on biomechanical and fluid properties of blood and blood cells, such as erythrocyte deformability and aggregation, change in the concentration of basic plasma components (fibrinogen, albumins, globulins, testosterone, etc.), changes in blood flow (through vasodilatation and change in overall blood viscosity) changes in blood volume, changes in the endothelial cells of the vascular walls, changes in blood pressure, changes as a result of tissue hypoxia, interactions and different hemorheological changes. The multiple hemorheological, physiological and PBM effects during physical activity and their interconnectedness and strength make their differentiation very difficult. Hence, separating the PBM effect and pure physiological effects of applied physical activities would be of interest [24].
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Finally, other parameters such as pain, pain pressure threshold, elastic properties of tissue, circadian variation of blood pressure, quality of life and psychological factors should be further studied in athletes after a PBM intervention, as they have been shown to be improved after a whole-body PBM treatment in populations suffering from chronic pain [25,26,27].
This entry is adapted from the peer-reviewed paper 10.3390/app13053147
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