Lifting lighter weights might make slow-twitch muscle fibers grow more than lifting heavier weights, but scientists aren't totally sure yet because the results aren't clear.

Lifting heavier weights might make your fast-twitch muscle fibers grow more than lighter weights, but the results aren't totally certain.

Lifting lighter weights with more reps might make your slow-twitch muscles grow bigger than lifting heavier weights with fewer reps.

Lifting heavy weights might help you build slightly more muscle than lifting light weights if you're new to training, but the difference isn't big enough to say for sure it's real.

Lifting heavier weights might help you get stronger a bit more than lifting lighter weights, but the difference is so small that we can’t be sure it’s real — it could just be luck.

We just don’t know yet if light or heavy weights make muscles grow better — the results could swing either way in future studies, so we need more research.