When young women who don't exercise start lifting weights, using medium or heavy weights didn't make their arms grow differently, but their legs did grow more with one type. This might be because...

Using light weights for arm exercises can make your arms slightly more muscular, but using light or heavy weights for leg exercises doesn’t change leg muscle size in young women who haven’t trained before.

Lifting heavy weights makes your legs much stronger than lifting light weights, but for your arms, both heavy and light weights make you about equally stronger.

When lifting weights with your arms, whether you use heavy or light weights, you get about the same improvement in how many reps you can do with both heavy and light weights.

For women who already lift weights, slowly increasing how many sets they do every couple of weeks doesn’t help them build thicker thigh muscles any more than just keeping their workout the same over 12 weeks.

Doing partial reps with extended muscle stretch and full reps with normal movement build your arm and thigh muscles about the same amount over 12 weeks — neither one is clearly better than the other.