Intravascular Laser Irradiation of Blood (ILIB) is a low-level laser technique, that has systemic effects, including activation of the antioxidant system, inhibition of the systemic inflammatory process, increased blood fluidity and hemorrheological property on the red cells. However, the use of ILIB as an ergogenic resource in sports is little studied.

To investigate the acute influence of ILIB on muscle power and heart rate variability (HRV), in physically active individuals submitted to a submaximal effort test.

The study is a randomized controlled crossover clinical trial. Nine male participants, university students, with a mean age of 24 ± 4.52 years and practitioners of regular physical activity were evaluated. The volunteers participated in the two intervention groups (ILIB and placebo) at different times. First, an evaluation session was carried out, being identified HRV indicators and blood lactate level at rest and in response to the stress test. After seven days, the participants received a session of the experimental protocol, which was drawn. After finishing these sessions, a reassessment was performed, getting data on HRV indicators and blood lactate level at rest and in response to the exercise test. After seven days, the entire data collect was repeated, however, the participants performed the remaining experimental protocol. The results were analyzed using Two-Way ANOVA with repeated measures, complemented with the Bonferroni test. All conclusions were obtained at the 5% significance level.

For the physical performance variables, the Fatigue Index showed a significant difference (p<0.05) from the Post-Placebo moment (54.5±13.9) in relation to the Post-ILIB (45.1±9.9). Blood lactate showed a significant difference between moments (initial, post-test and after 15 min) within all groups. For HRV, in the time domain, the indices showed a significant difference (p<0.05) when comparing the moments within the interventions in relation to the initial moment. Furthermore, the RMSSD values were different between Pre-ILIB (3.54±0.44) against Post-ILIB (4.22±0.27); after the Wingate test, the Pre-Placebo (1.00±0.31) differed from the Post-Placebo (1.77±0.74). In the frequency domain, HF and LF/HF showed a significant difference (p<0.05) from Post-ILIB to Pre-ILIB after 15 min.

The study showed a possible relationship between the acute influence of the use of ILIB on parasympathetic activity. It did not show improvement in performance in an anaerobic test, but suggested a possible improvement in the ability to withstand high-intensity stimuli. The lack of ILIB studies in sports science, as well as the study's findings, suggest that more research should be done, using different protocols with different stimuli.

The ILIB can be useful for coaches and health professionals working with athletes, helping to optimize physical recovery, making it a resource for post-training recovery.