Effect of photobiomodulation on quadriceps strength and endurance in healthy adults: a double-blind randomized controlled trial

Purpose: To explore the effect of photobiomodulation on quadriceps strength and endurance torques in healthy adults.
Methods: Twenty-eight physically inactive healthy adults were randomized to one of two interventions: photobiomodulation (n = 14) or sham (n = 14). Quadriceps strength was evaluated by maximum voluntary isometric contraction tests across three knee extension angles (60°, 70° and 80°) and endurance by an elastic resistance in multiple-set knee extension/flexion repetitions using a load cell. The outcomes were measured at three timepoints, (i) pre-baseline, (ii) baseline, and (iii) final assessment. The photobiomodulation was applied to the quadriceps and triceps surae muscles of the dominant lower limb, using a cluster with 1 infrared laser diode and 3 led amber of 170 mW for 240 seconds over four consecutive days. The sham group went through the same procedures, but the equipment was off, both patients and assessor were blinded to the intervention. Reliability and minimal detectable change of the measures were obtained from the pre-baseline and baseline timepoints. Comparisons between the intervention effects were completed using analysis of covariance with baseline data as covariates with an intention-to-treat approach.
Results. There were no differences between photobiomodulation and sham for maximum isometric at 60°, 70°, 80° and endurance torques (mean difference [95% confidence interval] = 0.008[-0.29;0.31], 0.32[-0.32;0.69], 0,007[-0.35;0.36] and 0.04[-0.03;0.12], respectively). The mean difference between intervention groups were lower than the minimal detectable change for the maximum isometric torque and endurance torque.
Conclusion: Photobiomodulation does not change quadriceps strength and endurance compared to sham in healthy adults.