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.

All the studies looked only at leg muscles in young people — we don’t know if the same results apply to arms, women, or older adults.

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.

There are only a few small, short studies on this topic, and many didn’t even track whether people stuck to their workout plans — so we can’t trust the results very much.

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 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.