Most people grow muscles well with both heavy and light weights, but a few might grow better with one than the other — it’s rare and not predictable.

Some people’s muscles get stronger in a way that matches the weight they trained with—light weights help more with light tasks, heavy weights help more with heavy tasks—but this doesn’t happen the same way in every part of the body, so you can’t always predict it.

Some people’s muscles grow better with heavy lifting, others don’t care as much — this study found that even when using heavy weights, some people responded better to one version than another, showing that not everyone reacts the same way.

People’s muscles grow differently no matter if they lift heavy or light weights — some grow a lot, some grow little, but it’s not because of the weight; it’s because of their body’s natural differences, and you can’t reliably predict who will respond better to heavy vs. light lifting.

Some people build muscle the same way no matter if they lift heavy or light weights, but others—especially those who already train a lot—build more muscle with light weights and restricted blood flow, showing that not everyone reacts the same way.

Most people gain muscle just as well with light or heavy weights if they train hard to exhaustion, but a few might respond better to one over the other—though we can’t reliably tell who those people are.