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.

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.

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.

When untrained men perform cable curls, the amount of muscle growth in the biceps does not change significantly whether the shoulder is extended to increase tension on the muscle, as long as the resistance and effort level remain the same.

In untrained young women, doing biceps curls with both arms at the same time or one arm at a time leads to the same amount of muscle growth in the upper arm after 8 weeks, suggesting that how much total muscle is activated during the exercise does not control how much the muscle grows.

Different ways of performing biceps curls lead to small but detectable differences in how much muscle grows in specific areas and how much strength improves for that movement.