Bimagrumab is a fully human monoclonal antibody (IgG1/λ) designed to block the activin type II receptors (ActRII). It functions as a potent and selective antagonist that binds to ActRIIA and ActRIIB with high affinity, thereby inhibiting the binding of several negative regulators of muscle growth, including myostatin (GDF-8), activin A, and GDF-11. By blocking this signaling pathway, bimagrumab aims to promote skeletal muscle hypertrophy and increase muscle mass and strength. It has been investigated in clinical trials for conditions involving muscle wasting and weakness, such as sporadic inclusion body myositis (sIBM), sarcopenia, and obesity with mobility limitation. While it demonstrated significant increases in lean body mass, its development for sIBM was discontinued after Phase II/III trials did not meet the primary functional endpoint.