There is evidence about the effects of photobiomodulation therapy (PBMT) alone and combined with static magnetic field (PBMT-sMF) on skeletal muscle fatigue, physical performance and post-exercise recovery in different types of exercise protocols and sports activity. However, it is unknown the effects of PBMT-sMF to improve the subsequent performance after a first set of exercise. Therefore, the aim of this study was to investigate the effects of PBMT-sMF, applied between two sets of exercises, on the subsequent physical performance.

A randomized, crossover, triple-blinded (assessors, therapist and volunteers), placebo-controlled trial was carried out. Healthy non-athletes' male volunteers were randomized and treated with a single application of PBMT-sMF and placebo between two sets of an exercise protocol performed on isokinetic dynamometer.

The order of interventions was randomized.

The primary outcome was fatigue index, measured by isokinetic dynamometer during the exercise protocol. The secondary outcomes were total work and peak torque measured by isokinetic dynamometer during the exercise protocol; and blood lactate, measured by blood samples collected before, 3 minutes after the first set of the exercise protocol, 3 minutes after the application of the intervention and 3 minutes after the second set of the exercise protocol.

Statistical analysis:

The findings were tested for normality using the Kolmogorov-Smirnov test and were determined to have a normal distribution. Data were expressed as the mean and standard deviation, and a two-way repeated measures ANOVA was performed to test between-group differences at each timepoint (treatment effects), mean difference (MD) and 95% confidence intervals (CI), followed by the Bonferroni post hoc test. The significance level was set at p < 0.05.

Inclusion criteria:

• Male healthy volunteers;
• Non-athletes or those who practiced physical activity up to once a week;
• Aged 18-35 years.

Exclusion criteria

• History of musculoskeletal injuries in the hip and knee regions in the two months prior to the study;
• Use of pharmacological agents and nutritional supplements;
• Chronic joint disease in the non-dominant lower limb.

Data will be shared upon request addressed to the principal investigator.

A researcher programmed the device (placebo or PMBT-sMF) and was instructed not to inform the volunteers or other researchers as to the type of treatment (placebo or PBMT-sMF). Therefore, the researcher responsible for the treatment was blinded to the type of treatment administered to the volunteers. The sounds and signals emitted from the device as well as the information displayed on the screen was identical, regardless of the type of treatment (placebo or PBMT).