You can build muscle by working one arm or leg at a time, even if your body doesn’t show higher levels of muscle-building hormones in your blood—so maybe it’s the physical stress on the muscle itself, not the hormones, that makes it grow.

Working out until you're exhausted might make your body release more growth hormone and testosterone, which could help your muscles grow — but we’re not sure if these hormones actually cause the growth.

When you train one arm or leg with weights, the other arm or leg doesn't get stronger or bigger—even though your body is adapting in other ways. This suggests those body-wide changes aren't enough to build muscle in the side you didn't train.

Even though lifting weights makes your body release growth hormone and testosterone, studies show that these short-term hormone surges don’t actually make your muscles grow bigger over time.

Just because your testosterone, growth hormone, and IGF-1 levels spike after a workout doesn't mean those spikes are what make your muscles grow.

Even though lifting weights with short breaks makes your body release more growth hormone, that doesn’t mean you’ll grow bigger muscles over time.