Myostatin is a naturally occurring protein that inhibits skeletal muscle growth.

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

When scientists blocked a protein called myostatin in people, their muscles got bigger — which means myostatin normally keeps muscles from growing too much. So yes, it’s a natural brake on muscle growth.

Study: Humans with function-disrupting variants in the myostatin gene (MSTN) have increased skeletal muscle mass and strength, and less adiposity

People born with a broken version of the myostatin gene have more muscle and less fat than others, which means myostatin normally stops muscles from growing too big.

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

When scientists blocked a protein called myostatin in mice, their muscles got bigger and stronger — which means myostatin normally stops muscles from growing. So yes, it’s a natural brake on muscle growth.

Study: GDF8 and activin A blockade protects against GLP-1–induced muscle loss while enhancing fat loss in obese male mice and non-human primates

Myostatin is like a natural brake on muscle growth — when scientists turned off this brake in mice and monkeys, the animals kept more muscle and even grew more, proving myostatin normally stops muscles from getting bigger.