['We investigated the effects of electrical stimulation and low-intensity laser (LIL) energy on the mitochondrial function of cultured C2C12 myotubes in order to find a dosage that could be used to improve the function of mitochondria, and then rehabilitate exercise-induced damage and fatigue.', 'Many other studies in the past demonstrated that LIL had a cytoprotective effect, and a recent study also found that LIL could reduce muscular fatigue during tetanic contractions in rats.', 'Cultured C2C12 myotubes were subjected to electrical stimulation or/and LIL irradiation at various intensities. Reactive oxygen species (ROS) were detected with a fluorescent probe (DCFH-DA) and mitochondrial function was assessed with an MTT assay.', 'The results showed that electrical stimulation at 20 ms, 5 Hz, and 45 V for 75 min can induce mitochondrial dysfunction in cultured C2C12 myotubes. Electrical stimulation-induced mitochondrial dysfunction was improved, but degeneration occurred with LIL at doses of 0.33-8.22 and 11.22-14.16 J/cm2, respectively, and these changes were markedly increased with LIL at 0.33 and 1.34 J/cm2, respectively.'] Does low-intensity laser irradiation improve the mitochondrial dysfunction of C2C12 induced by electrical stimulation?