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This study investigated the effects of a CoCl2-simulated hypoxic environment on the muscle fiber switching signaling pathways calcineurin A/nuclear factor of activated T cells cytoplasmic 1 (CnA/NFATc1) and myostatin. In this study, C2C12 muscle cells were cultured in vitro under CoCl2-simulated chemical hypoxic conditions, the expression levels of CnA and myostatin were detected through qRT-PCR and Western blot analyses, and a positioning study of NFATc1 was carried out by immunofluorescence labeling. Results showed that CoCl2 treatment significantly increased the expression levels of CnA and myostatin. Moreover, the position of NFATc1 expression changed; actually, its expression in the nucleus considerably increased. Furthermore, CoCl2-induced hypoxia inhibited the differentiation of C2C12 cells and reduced the expression levels of many slow- and fast-twitch muscles marker genes, but immunofluorescence staining results showed that the proportion of MyHC I type muscle fiber increased after CoCl2 treatment. The hypoxic environment simulated by CoCl2 can activate the signaling pathways CnA/NFATc1 and myostatin and increases the proportion of MyHC I type muscle fibers.