Influence of irradiance on photobiomodulation therapy for muscle performance in healthy individuals in a strength training program for lower limbs. A double-blind randomized controlled trial

This investigation attempts to elucidate power density's interplay with observed outcomes subsequent to a training regimen. Forty-two participants were stratified into three groups (Sham, Cluster, LED-Blanket), with irradiated groups receiving 300 J of energy under distinct parameters. Photobiomodulation irradiation was applied to the quadriceps and hamstrings before each of the ten prescribed training sessions, which consisted of three sets of stiff and squats. Participants underwent assessment during sessions, encompassing blood lactate measurements and psychophysiological scales (Numerical Rating Pain Scale for Pain and Rate of Perceived Effort). Additionally, pre-intervention, post-intervention, and follow-up evaluations on an isokinetic dynamometer measured peak torque. Two-way repeated measures ANOVA for intra- and inter-group comparisons. No significant inter-group differences or group-time interactions were discerned in lactate concentration or psychophysiological indices. Solely, a difference surfaced in the peak torque of the dominant limb during knee flexion, manifesting across pre-, post, and follow-up intervals (p = 0.003 and p < 0.001) with an effect size of n(2) = 0.080. Within the outlined methodological framework, photobiomodulation was ineffective in eliciting performance enhancements, with divergent parameters evincing equivocal efficacy.