Lifting heavy weights puts stress on your muscles, which is thought to be a main reason they get bigger and stronger.

People grow muscle at very different rates — but each person tends to grow their arms and legs similarly, no matter what weight they use. This means your genes and biology matter more than how heavy your weights are.

When people lift weights until they can't do another rep, their muscles grow about the same amount whether they use heavy or light weights — and how much they grow depends more on their own body than on how heavy the weights are.

When you train hard enough to fail on every set, how heavy the weights are matters less than your body’s natural ability to grow muscle.

When people lift weights until they can't anymore, their muscles grow just as much whether they use heavy or light weights, as long as they push to their max. This shows that how hard you try matters more than how heavy the weights are.

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.