Myostatin-inhibiting antibodies increase muscle mass in preclinical models by directly blocking signaling pathways that limit muscle growth.

Study: GDF8 and activin A are the key negative regulators of muscle mass in postmenopausal females: a randomized phase I trial

Scientists gave people special antibodies that block a protein (myostatin) that normally stops muscles from growing. The result? People’s thigh muscles got about 6% bigger while they were taking the treatment — proving that blocking myostatin really does make muscles grow.

Study: Anti-myostatin antibody increases muscle mass and strength and improves insulin sensitivity in old mice

Scientists gave mice a special antibody that blocks a signal telling muscles to stop growing. The mice got stronger and their muscles got bigger, proving the antibody works like a 'stop sign' remover for muscle growth.

Study: Blocking extracellular activation of myostatin as a strategy for treating muscle wasting

Scientists gave mice a special antibody that stops a protein called myostatin from telling muscles to stop growing. The mice’s muscles got 17.5% bigger and stronger, without getting weaker — proving the antibody works like it’s supposed to.

Study: ACE-031, a soluble activin type IIB receptor, increases muscle mass and strength in the common marmoset (Callithrix jacchus)

This study gave monkeys a drug that blocks a natural signal that stops muscles from growing, and their muscles got bigger and stronger — just like the claim says.