This invention is in the field of anti-Activin receptor IIB (ActRIIB) antibodies. In particular, it relates to the use of said antibodies for treating muscle disorders, such as muscle wasting due to disease or disuse.本發明係關於抗活化素受體IIB(ActRIIB)抗體領域。特定言之,本發明係關於該等抗體用於治療肌肉病症(諸如因疾病或不使用之肌肉萎縮)的用途。