If you're a guy new to lifting, doing bicep curls with your arms in front of you or behind you gives your brachialis muscle (a hidden arm muscle) about the same growth — around 8–10% after 10 weeks....

Doing bicep curls with your arm in front of your body or behind your body gives you the same muscle growth and strength gains if you're using the same amount of weight and doing the same number of reps.

The muscle underneath your bicep gets just as strong and big whether you curl with your arm in front or behind you.

If you're a guy new to lifting, doing bicep curls with your arms in front of you or behind you doesn’t really make a difference in how much your biceps grow — both ways work about the same.

For guys new to lifting, doing bicep curls with your arms in front of your body works just as well for building arm muscle as doing them with your arms behind you — both give about the same 6% to 9% growth in 10 weeks.

In untrained men performing cable curls with the same resistance, movement range, and effort, changing the shoulder angle between neutral and fully extended positions leads to similar increases in elbow muscle thickness after 10 weeks of training.