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.

After 12 weeks of training with the same total workload, neither method made the biceps noticeably thicker than the other.

Women who did any kind of upper-body strength training ended up with thicker biceps than women who didn’t train their upper body at all.

Doing bicep curls with two different methods—either lowering the weight gradually or keeping it heavy—both made the upper arm muscles thicker in young women after 12 weeks of training.

If untrained adult men lift weights twice a week for 8 weeks, doing 4-6 sets of 8-12 reps until they can't do any more, their upper arm muscles will get bigger - this is measurable with ultrasound or other imaging.

Doing regular weightlifting reps with full rest between sets builds a tiny bit more arm muscle than doing drop sets on a smart machine, but the difference is so small it doesn’t really matter in real life.