BACKGROUND: Low-level laser therapy (LLLT) has been demonstrated to be effective in optimizing skeletal muscle performance in animal experiments and in clinical trials. However, little is known about the effects of LLLT on muscle recovery after endurance training. OBJECTIVE: This study evaluates the effects of low-level laser therapy (LLLT) applied after an endurance training protocol on biochemical markers and morphology of skeletal muscle in rats. METHOD: Wistar rats were divided into control group (CG), trained group (TG), and trained and laser irradiated group (TLG). The endurance training was performed on a treadmill, 1 h/day, 5 days/wk, for 8 wk at 60% of the maximal speed reached during the maximal effort test (Tmax) and laser irradiation was applied after training. RESULTS: Both trained groups showed significant increase in speed compared to the CG. The TLG demonstrated a significantly reduced lactate level, increased tibialis anterior (TA) fiber cross-section area, and decreased TA fiber density. Myogenin expression was higher in soleus and TA muscles in both trained groups. In addition, LLLT produced myogenin downregulation in the TA muscle of trained animals. CONCLUSION: These results suggest that LLLT could be an effective therapeutic approach for stimulating recovery during an endurance exercise protocol.

Background: The effectiveness of low-level laser therapy in muscle regeneration is still not well known. Objective: To investigate the effects of laser irradiation during muscle healing. Method: For this purpose, 63 rats were distributed to 3 groups: non-irradiated control group (CG); group irradiated at 10 J/cm² (G10); and group irradiated at 50 J/cm² (G50). Each group was divided into 3 different subgroups (n=7), and on days 7, 14 and 21 post-injury the rats were sacrificed. Results: Seven days post-surgery, the CG showed destroyed zones and extensive myofibrillar degeneration. For both treated groups, the necrosis area was smaller compared to the CG. On day 14 post-injury, treated groups demonstrated better tissue organization, with newly formed muscle fibers compared to the CG. On the 21st day, the irradiated groups showed similar patterns of tissue repair, with improved muscle structure at the site of the injury, resembling uninjured muscle tissue organization. Regarding collagen deposition, the G10 showed an increase in collagen synthesis. In the last period evaluated, both treated groups showed statistically higher values in comparison with the CG. Furthermore, laser irradiation at 10 J/cm2 produced a down-regulation of cyclooxygenase 2 (Cox-2) immunoexpression on day 7 post-injury. Moreover, Cox-2 immunoexpression was decreased in both treated groups on day 14. Conclusions: Laser therapy at both fluencies stimulated muscle repair through the formation of new muscle fiber, increase in collagen synthesis, and down-regulation of Cox-2 expression.

BACKGROUND: Low-intensity pulsed ultrasound (LIPUS) has been shown to stimulate tissue metabolism and accelerate muscle healing. However, the optimal parameters in the use of LIPUS are still not clear. OBJECTIVE: The aim of this study was to analyze the effects of LIPUS on muscle healing in rats subjected to a cryolesion. METHOD: Twenty rats were divided into the following groups: an injured control group (CG) and an injured treated group (TG). Both groups were divided into 2 sub-groups (n=5 each) that were sacrificed 7 and 13 days post-surgery. Treatments were started 24 hours after the surgical procedure and consisted of 3 or 6 sessions. After euthanasia, the muscles were submitted to standard histological procedures. RESULTS: Qualitative analyses were based on morphological assessments of the muscle. The histopathological analysis on day 7 revealed that the muscles in the CG and the TG presented an intense inflammatory infiltrate, a large necrotic area and a disorganized tissue structure. After 13 days, both the CG and the TG had granulation tissue and newly formed fibers. The TG presented a more organized tissue structure. The quantitative analysis of collagen indicated similar findings among the groups, although the qualitative analysis revealed a better organization of collagen fibers in the TG at 13 days. The immunohistochemical analysis indicated that, at both time points, the expression of cyclooxygenase-2 was upregulated in the TG compared to the CG. CONCLUSIONS: LIPUS used as a treatment for muscle injury induced a more organized tissue structure at the site of the injury and stimulated the expression of COX-2 and the formation of new muscle fibers.

CONTEXTUALIZAÇÃO: Recursos eletrofísicos, como o ultrassom (US) e a terapia laser de baixa potência (LLLT), vêm sendo cada vez mais utilizados na prática fisioterapêutica. Estudos sugerem que esses recursos são capazes de estimular a proliferação de osteoblastos e a osteogênese no local da fratura, promovendo maior deposição de massa óssea e acelerando o processo de consolidação. OBJETIVO: Analisar os efeitos do US e da LLLT no processo de consolidação óssea por meio das análises biomecânica e histológica do calo ósseo. MÉTODOS: Foram utilizados 30 ratos machos, distribuídos aleatoriamente em três grupos: grupo controle fratura, sem tratamento (GC); grupo fratura tratado com US pulsado com burst de 1,5 MHz, 200us, 1KHz, 30 mW/cm² (GUS) e grupo fratura tratado com laser 830nm, 100mW, 120J/cm² (GL). Foram realizados defeitos ósseos circulares com broca de 2 mm de diâmetro nas tíbias dos animais. Os tratamentos foram realizados a cada 48 horas, totalizando sete aplicações e, no 14º dia, os animais foram sacrificados. A tíbia direita foi designada para análise biomecânica, enquanto a esquerda, para análise histológica. RESULTADOS: A análise biomecânica não mostrou diferença estatisticamente significativa entre as propriedades biomecânicas do GC, GL e GUS. Na análise morfométrica, tanto GUS quanto GL apresentaram área de osso neoformado estatisticamente maior em relação ao GC. No entanto, quando as duas modalidades de tratamento foram comparadas, não foram encontradas diferenças estatísticas entre elas. CONCLUSÃO: Ambos os recursos utilizados neste estudo foram capazes de acelerar o processo de reparo ósseo em ratos.

BACKGROUND: Electrophysical agents such as Ultrasound (US) and low-level laser therapy (LLLT) have been increasingly used in physical therapy practice. Studies suggest that these devices are able to stimulate osteoblast proliferation and osteogenesis at the fracture site, resulting in a greater deposition of bone mass and speeding up the consolidation process. OBJECTIVE: The aim of this study was to analyze the effects of US and LLLT on the bone healing process, through biomechanical and histological analysis of the bone callus. METHODS: A total of 30 rats were randomly allocated into three groups: control group fracture without treatment (GC); fracture group treated with pulsed US, burst 1.5 MHz, 200us, 1KHz, 30 mW/cm² (GUS) and fracture group treated with laser 830nm, 100mW, 120J/cm² (GL). Bone defects were performed with a circular drill of 2mm in diameter in the animal's tibias. The treatments were carried out after surgery consisting of 7 applications every 48 hours. After 14 days the animals were sacrificed and the tibias were removed to perform the analysis, being the right tibia designated for biomechanical analysis, while the left tibia for histological analysis. RESULTS: The biomechanical analysis showed no statistically significant difference between biomechanical properties of the CG, CL and GUS. In morphometric analysis, both GUS and GL showed a significantly higher woven bone tissue area compared to the control group. However, when the two treatment modalities were compared, there were no statistical differences between them. CONCLUSION: Both devices used in this study were able to accelerate the bone healing process in rats.