Lifting light or heavy weights until failure doesn’t clearly make your fast-twitch muscle fibers bigger in your thighs — the data is too mixed to say one is better.

Whether you lift light weights or heavy weights until you can't do another rep, your slow-twitch muscle fibers in your thighs grow about the same amount — but we can't be sure because the results are too uncertain.

We can’t say whether light or heavy weights are better for growing muscle fibers in the thighs — we just don’t have enough good data yet, and we need more studies with more people.

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.

Even if you lift light weights, if you go until you can’t do another rep, your muscles end up using almost all the same fibers as if you lifted heavy — which might be why both ways make muscles grow similarly.

If you're already someone who lifts weights, doing light weights twice a week until you can't do more reps can make your muscles bigger and stronger in just 8 weeks.