Influence of Power and Wavelength on Photobiomodulation Therapy for Muscle Performance in Healthy Subjects

In recent years, photobiomodulation has been studied as a means of increasing muscle performance in athletes and healthy individuals. This is possible due to the physiological changes that photobiomodulation therapy can promote. Moreover, given a large number of existing studies on the subject, some directions for future research have been established. For example, future research was established, the relationship between power and time because with high power, it will achieve the same energy with shorter application times. However, irradiation may not be offered for the minimum recommended time. Therefore, this study aims to compare different powers and, consequently, different application times for muscle performance in healthy individuals. For this, 42 participants will be recruited, males between 18 to 40 years old, without recent musculoskeletal injury or cardiorespiratory problems. The participants will participate in 3 evaluations containing functional and physiological variables and ten training sessions of lower limbs with previous photobiomodulation therapy application, comparing devices with a power of 0.864W and 1.864W. 0.864W and 1.2W. Lower limbs training will be composed of stiff and squat exercises twice a week, for five weeks. In the pre- and post-intervention evaluations, the following parameters will be evaluated isokinetic apparatus, body composition, and functionality of the vertical jump. For data analysis, we will use a normality test to verify the distribution and statistical tests will be used for intra and intra and intergroup comparisons, considering two factors in the comparisons time and group. A significance level of 5% will be adopted.

It is a blinded randomized clinical trial. The volunteers will undergo pre-evaluation, 5 weeks of training associated with the LED application, being distributed in two applications per week, and a re-evaluation 24 hours after the last application, totaling a total of approximately 7 weeks. Thus, on the first day (Pre-test) volunteers will be submitted to anthropometric evaluation and evaluation by bioimpedance for analysis of detailed body composition. Then, the maximum voluntary contraction test (CVM) will be performed on the isokinetic dynamometer, together with the electromyographic evaluation. Before and after the evaluation with the isokinetic dynamometer, thermography will be collected. Still, will be evaluated the vertical jump test after 15 minutes of passive rest.

After the initial evaluations, the researcher will go apply the respective interventions, which consist of applying LEDs all over the quadriceps and hamstring bilaterally, while the sham group (GS) will receive the LED application off, without the emission of light. The application will occur for five weeks and will occur twice weekly, on days spaced for at least 48 hours. The same will be done in conjunction with the lower limb strength training protocol. It is noteworthy that although the therapy follows the same energy values, two different pieces of equipment will be used, thus changing the wavelength, total power and power density, and the consequent coverage time and area.

The tests performed at the time of pre-application of the LED (Pre-test) will be reapplied in the same order 24 hours after the last application of the interventions. After seven days of the last application, the isokinetic evaluation, electromyography, and vertical jump evaluation will be performed. In addition, at the end of the second and fourth weeks, the volunteer will carry out an evaluation with the isokinetic dynamometer, electromyography, plethysmography, and thermography.

Eligibility Criteria:
Inclusion Criteria:

- healthy individuals;

Exclusion Criteria:

* musculoskeletal injury in the last three months;
* cardiovascular diseases;
* use of anabolic, anti-inflammatory and analgesic drugs 72 hours before the evaluations;
* use of alcohol and illicit drugs during the collection period;