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.

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 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 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 heavy weights, your muscles grow bigger because your body turns on a special chemical signal (mTORC1) that helps make more muscle proteins and building tools, letting your muscles grow faster.

When you lift weights, it's the pulling force on your muscles—not the tears or burn—that makes them grow bigger, and scientists think a specific molecular signal inside the muscle cells is behind this growth; other things like soreness or muscle burn probably don't cause the growth on their own.