## 4 Discussion  
To the best of our knowledge, this is the first study to evaluate redox metabolism to the application of PBMT-sMF in C2C12 muscle cells at both normal and H2O2-exposed conditions. It has demonstrated that PBMT-sMF can modulate COX activity, \(\Delta\)Ym, and ROS production, potentially activating cellular signaling pathways associated with a stress response. In research aimed at developing new therapeutic approaches, it is essential to consider a treatment's safety and efficacy. In this context, it has been previously shown that PBMT can stimulate cellular metabolism when administered within an ideal therapeutic dose window. However, when administered outside this therapeutic range, the effect is either minimized or nullified, resulting in bioinhibition and characterizing a dose-dependent response profile [31]. In this study, a dose-dependent response profile in cell viability was observed. Similarly, this behavior was found in other models and cell lines, such as primary neurons [32] and fibroblasts [33]. Data demonstrate that doses above 60 J, within the parameters used, do not positively affect C2C12 myoblast culture. Supporting our findings, [PERSON] et al. [34] evaluated the effect of PBMT at 1, 3, and 10 J in a Duchenne muscular dystrophy mouse model and found a dose-dependent response profile. The authors observed a significant increase in the gene and protein expression of dystrophin and a decrease in morpho-pathological aspects at 3 and 10 J, in addition to improved performance using 10 J compared to the control. Another recent study using PBMT-sMF at 1, 3, 10, and 30 J reported a prophylactic effect with no deleterious impact during the aging process in muscle tissue after short-term (15 weeks) and long-term (60 weeks) treatment in aged rats [35]. Cell viability measured by the tetrazolium salt (MTT) assay assesses the activity of dehydrogenase enzymes and is closely related to cellular energy metabolism and the consequent production of ROS, particularly by mitochondria [36]. At elevated levels of ROS, membrane permeabilization may occur along with damage to lipids and proteins. Damage to the cell membrane and consequently to DNA through double-strand breaks are major causes of apoptosis and cellular senescence [37]. The effect of PBMT (red LED at 658 nm) on the release of dsDNA in the extracellular medium was assessed in a recent study [38]. The authors irradiated different doses of PBMT (1.6 J and 7.2 J) in fibroblasts under normal (non-stressful) conditions, examining the effects at 24, 48, and 72 h after exposure. The results demonstrated a greater release of dsDNA after 24 h only in the group irradiated with 1.6 J. However, no statistically significant differences were observed after long exposure periods (48 and 72 h) at 7.2 J. In the present study, the release of dsDNA into the extracellular medium was evaluated and no differences were observed. It is known that isolated PBMT can affect the permeability of the nuclear membrane. However, cells have repair mechanisms, which the combined use of PBMT-sMF may have triggered. Although cellular repair was not evaluated, the analysis of apoptosis by flow cytometry can, in part, explain this. Recent studies support the idea that isolated PBMT can modulate the production of ROS, which is one of the mechanisms contributing to the regeneration of injured muscle tissue. This effect has been observed in experimental studies in both humans [9; 39] and animal models [8], following exercise and in muscle injury models. Evidence also indicates that moderate-intensity electromagnetic fields (1 mT-1 T) reduce oxidative stress and promote myogenic cell differentiation and hypertrophy [40]. In the present study, a modulatory effect was found on ROS production in muscle cells when treated with PBMT-sMF and exposed to H2O2. The production of these species generated by H2O2 exposure was regulated, returning to control levels.