Photobiomodulation therapy (PBMT) has recently been indicated as a potential therapeutic strategy in diverse health and sports contexts. However, its efficacy on muscle performance in female futsal players remains unknown. The purpose of this study was to investigate the dose-response effect of PBMT on muscle performance in female futsal players.

Background: Photobiomodulation therapy (PBMT) has recently been indicated as a potential therapeutic strategy in diverse health and sports contexts. However, its efficacy on muscle performance in female futsal players remains unknown. The purpose of this study is to investigate the dose-response effect of PBMT on muscle performance in female futsal players. Methods: In a crossover design, fifteen female futsal athletes (age: 18-30 years) will be randomized to receive 1 of 4 PBMT conditions (placebo, 300, 900, and 1260 joules [J]) on four occasions, separated by a 2-wk washout period. PBMT treatments will be applied on the quadriceps muscle of both legs using a device containing 200 light-emitting diodes (LEDs), immediately before the following tests (dependent variables): countermovement jump (CMJ) (i.e., flight time as indicator of muscle power), maximum voluntary isometric contraction (MVIC) for the leg extension exercise (i.e., muscle strength), and 3 sets of repetitions-to-failure (i.e., local muscular endurance) for the 45º leg press exercise, with recording of rating of perceived exertion (RPE) after each set. The fatigue index will be determined by the number of repetitions between sets 1 and 3. Statistical analyses will be performe using IBM SPSS Statistics for Windows (version 24.0; IBM Corp., Armonk, NY). Data will be tested for normality and homogeneity using the Shapiro-Wilk's and Levene's tests, respectively. One-way ANOVA tests will be performed to evaluate the differences in the fatigue index, flight time, and peak and mean torque between the treatment conditions (placebo, 300, 900, and 1260 J). Changes over time and between treatment conditions in maximum number of repetitions and RPE will be analyzed with two-way repeated measures ANOVA. Violation of sphericity was corrected using the Greenhouse-Geisser method. When significant differences will be confirmed with the ANOVA, multiple comparison testing will be performed using the Bonferroni post hoc correction to identify these differences. Values will be expressed as mean (standard deviation and 95% confidence interval). The significance level was set at p < 0.05.

Inclusion Criteria:

• Age between 18 and 35 years
• Playing futsal regularly for more than 1 year.

Exclusion Criteria:

• Use of any ergogenic or anabolic supplement within 6 months prior to the start of the study,
• Take any medication that may affect the ability to perform the physical tests,
• Have any physical limitation (e.g. joint or muscle injury) that may affect the ability to perform the physical test,
• Be engaged in a restricted diet program (e.g. weight loss diet),
• Have any skin sensitivity or diseases (e.g. erysipelas, eczema, dermatitis, psoriasis and urticaria) in the irradiated area that may be aggravated by PBMT.