When you lift weights, the pulling force on your muscles is what makes them grow bigger—not because of hormones or feeling tired, but because your muscles sense the tension and respond by building more muscle fibers.

When you lift weights, the pulling force on your muscles is what makes them grow bigger—not because of hormones or feeling burned out, but because your muscles sense the tension and respond by building more muscle fibers.

When you lift weights, the physical pull on your muscles is the main reason they grow bigger — not because of hormones or feeling tired or burned out.

When you lift weights, the pulling force on your muscles is what makes them grow bigger—not hormones or feeling tired. This force turns on internal signals that tell your muscles to make more protein and get larger over time.

Lifting weights makes your muscles grow because the longer and harder you work them, the more they get the signal to build new muscle fibers.

When you lift weights, your muscles sense the tension and turn on internal signals that help them grow bigger—and they might even become better at using leucine, a protein-building block, to help with that growth.