The disclosure provides anti-myostatin antibodies and methods of making and using the same. Nucleic acids encoding the anti-myostatin antibodies and host cells comprising the nucleic acids are also provided. The anti-myostatin antibodies have uses that include treating a muscle wasting disease, reducing body fat accumulation, and increasing mass and strength of muscle tissue. The disclosure also provides polypeptides containing a variant Fc region and methods of making and using the same. Nucleic acids encoding the polypeptides and host cells comprising the nucleic acids are also provided. The polypeptides have uses that include suppressing the activation of immune cells; treating an immunological inflammatory disease, autoimmune disease, or viral infection; and increasing muscle mass and strength or reducing body fat accumulation.