Introduction: Low-level laser therapy (LLLT) is effective in preventing fatigue and in stimulating the microcirculation and cellular activity. In this study, we examined the effect of LLLT on injured tibial muscle in vivo by assessing muscle function during fatigue. Methods: Twenty-four male mice were used. Each mouse received an injection of sterile 0.9% saline solution (50 µL) in the right tibialis anterior muscle, after which the tendon of the muscle was exposed, connected to an isometric transducer and subjected to a resting tension of 1 g. A bipolar electrode was attached to the tibial nerve for electrical stimulation. The mice were randomly allocated to one of two groups: G1 (control: 3 h -n=8 and 9 h -n=5) and G2 (treated with GaAlAs laser, λ660 nm, 35 mW, 0.6 J, 17 s: 3 h -n=6 and 9 h -n=5). Results: In G1 mice, the amplitude of the tetanic contracture in response to induced fatigue remained unchanged during six consecutive tetani. The amplitude of the tetanic contractions in response to electrical stimulation (4-8 mV) was also unchanged. These results indicated muscle intactness in response to the load imposed by tetanus. In G2 mice, there was an increase in the amplitude of contraction after 3 h and 9 h when compared to G1 at 83% tetanus. Conclusion: These results indicate that exposure of muscle to LLLT enhanced the contractile force and increased the resistance to muscle fatigue without causing morphological damage to cellular structures.

Introduction: Envenomation by Bothrops snakes can produce local pain, edema, hemorrhage and myonecrosis.However, standard antivenom therapy is generally ineffective in neutralizing these effects so that alternative methods of treatment have been investigated. In experimental animals, low-level laser therapy (LLLT) attenuates the local effects of Bothrops venoms, but the benefits of LLLT on muscle function after envenomation are unclear. In this study, we examined the influence of LLLT on the contractile activity of mouse skeletal muscle injected with venom from Bothrops jararaca, the principal cause of snakebite in southeastern Brazil. Methods: Twenty-seven male mice were used. Mice were injected with venom (40 μg in 50 μl) in the right anterior tibialis muscle, after which the muscle tendon was exposed, connected to an isometric transducer and subjected to a resting tension of 1 g. A bipolar electrode was attached to the tibial nerve for electrical stimulation. The mice were randomly allocated to five groups: A -Control (n = 3), B -Venom 3 h (n = 6), C -Venom 9 h (n = 6), D -Venom + Laser 3 h (n = 6), E -Venom + Laser 9 h (n = 6). Results: The two groups that received LLLT post-venom showed improved muscle contraction and contracture in relation to muscle treated with venom alone. Conclusion: These results indicate that LLLT can improve muscle function after damage induced by B. jararaca venom.