Characterization of Skeletal Muscle Strain Lesion Induced by Stretching in Rats: Effects of Laser Photobiomodulation

Background: Unusual and exhaustive physical exercise can lead to muscle lesions depending on the type of contraction, intensity, duration, age, and level of conditioning. Different therapies have been proposed to prevent or reduce exercise-induced muscle damage. Objective: In this study, we investigate the effects of low-level laser therapy on skeletal muscle strain in an experimental model in rats. Materials and methods: Male Wistar rats (200g) were used. The animals were randomized into groups of six animals. We performed tibialis muscle elongation using a previously described protocol. The animals were anesthetized and submitted to passive stretching of the anterior tibial muscle attached to a weight corresponding to 150% of the body mass of the animal for 20min, rested for 3min, and received a second traction for 20min. The cytokines, tumor necrosis factor- (TNF-), interleukin-1 (IL-1), IL-6, and IL-10, edema, and C-reactive protein (CRP) levels were determined in the tibialis anterior muscle. Results: Plasma extravasation of groups treated with different doses of laser energy, lesion +1J (2.61 +/- 0.46), lesion +3J (2.33 +/- 0.13), lesion +6J (2.92 +/- 0.91), and lesion +9J (2.80 +/- 0.55), shows a significant reduction of extravasation when compared with the injury group (5.46 +/- 1.09). Laser therapy was able to significantly reduce CRP and cytokine levels (TNF-, IL-1, IL-6, and IL-10). Conclusions: Laser photobiomodulation reduced skeletal muscle edema as well as cytokines and CRP, leading to a significant reduction in inflammatory markers. (AU)