When you curl with your arms behind you, your biceps stretch more and grow more than when you curl with your arms in front.

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.

Just because a study doesn’t find a clear difference in arm muscle growth between two curl types, it doesn’t mean there isn’t a real difference — the study might just be too small to catch it.

If you're a guy new to lifting and do bicep curls with a cable machine for 10 weeks, your biceps grow evenly from top to bottom — not more in one spot — no matter how your shoulder is positioned.

Working your biceps with your arms stretched back might grow the upper part of the muscle a bit more than doing curls with your arms already in front of you.