When researchers measured the thickness of the upper arm at two specific spots, both spots got thicker after 12 weeks of arm workouts.

After doing bicep curls 24 times over 12 weeks, women’s upper arm muscles got noticeably thicker, no matter which way they did the curls.

When young women lift weights until they can't anymore, their arm and leg muscles get thicker by about 6-9% after 6 weeks. It doesn't matter if they lift heavy or light weights—both work the same for muscle growth.

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.

Whether you use light or heavy weights, your muscles can grow about the same amount if you train hard enough—both methods work for building muscle size.

When young women lift weights until they can't anymore, using lighter weights or heavier weights leads to about the same muscle growth in their arms and legs after 6 weeks.