Low-level light pre-conditioning promotes C2C12 myoblast differentiation under hypoxic conditions.

Exercise, especially anaerobic one, can gradually increase muscle mass over time as a result of adaptive responses of muscle cells to ensure metabolic homeostasis in the tissue. Low-level light therapy (LLLT) or photobiomodulation exhibits beneficial effects on promoting muscular functions, regeneration, and recovery from exhausting exercise, although the underlying cellular mechanisms remain poorly understood. We found that hypoxia, a condition following anaerobic exercise, significantly impeded myotube differentiation from myoblasts. However, this adverse effect was blunted greatly by pre-exposure of myoblast cells to a 980 nm laser at 0.1 J/cm2 , resulting in almost nearly normal myotube differentiation. LLL pre-treatment enhanced myotube formation by 80%, with a tubular diameter of 4.28 ± 0.11 μm on average, representative of a 53.4% increase over sham light treatment. The normalized myoblast differentiation concurred with 68% more mitochondrial mass and myogenin expression over controls. Moreover, LLL pre-treatment appeared to enhance glucose uptake, prevent energy metabolic switch from oxidative phosphorylation to glycolysis, and diminish lactate production under hypoxic conditions. The observation provides valuable guidance with respect to the timing of LLLT and its potential effects on muscle strengths in concert with anaerobic exercise.