Photobiomodulation therapy (PBMT) has recently been used to alleviate postexercise muscle fatigue and enhance muscle recovery, demonstrating positive results. A previous study by the investigator's research group demonstrated the optimal dose and the optimal output power (100 mW) for an infrared wavelength (810 nm). However, the effects of optimized PBMT on performance and post-exercise recovery in high-level soccer players, to date have not been evaluated.

The present research project aims to evaluate the effects of PBMT (using low-level laser therapy) applied before a progressive running test on functional, muscle damage, inflammatory and oxidative stress markers in high-level soccer players.

To achieve the proposed objective it will perform a randomized, crossover triple-blinded, placebo-controlled trial, with high-level soccer players as volunteers.

Twenty-two volunteers will be randomly allocated to two intervention groups: active or placebo PBMT before a progressive running test (ergospirometry test).

The blood samples for biochemical analysis will be obtained before and after a progressive running test, and another outcomes (functional) will be obtained during the test.

The data will be collected by a blind assessor. The statistical analysis will follow the intention-to-treat principles and data on functional analysis will be analyzed using the paired and two-tailed t-student test. Data on biochemical analysis will be analyzed using two-way ANOVA, followed by Bonferroni post hoc test.

The investigators will analyze: functional aspects (rates of oxygen uptake -VO2max (absolute and relative), aerobic and anaerobic threshold and time until exhaustion), muscle damage (creatine-kinase -CK and lactate dehydrogenase -LDH), inflammatory markers (IL-1β, IL-6 and TNF-α) and oxidative stress markers (Thiobarbituric acid -TBARS, catalase - CAT, superoxidedismutase - SOD and carbonylated proteins).

Inclusion Criteria:

• High-level soccer players;
• Age between 18 and 35 years;
• Male gender;
• Minimum of 80% participation in team practice sessions;
• Agreement to participate through signed statement of informed consent.

Exclusion Criteria:

• History of musculoskeletal injury to hips or knees in previous 2 months;
• Use of pharmacological agents or nutritional supplements;
• Smokers and alcoholics;
• Occurrence of musculoskeletal injury during the trial;
• Any change in practice routine in relation to rest of the team during the trial.

The mode of intervention (active or placebo photobiomodulation) will be coded by an independent researcher. The randomization schedule will contain only codes (not the actual intervention). The output from the laser device is exactly the same from either the active or the placebo interventions. These features will guarantee that participants, therapists and outcomes assessor will be blinded to the treatment arms.