If you're into weight training, where you position your shoulder affects how stretched your biceps are and how stiff they feel before exercising — especially when your arm is pulled back behind you.

After heavy bicep workouts, most guys show reduced muscle stiffness in a specific part of the bicep—especially when the arm is stretched out—meaning that area might get worked harder during certain movements.

Your bicep gets stiffer as you bend your elbow — but only if your palm is up or sideways. If your palm is down, it gets looser the more you bend.

Doing bicep curls with your arm stretched behind you makes the lower part of your bicep feel more strained right after the workout than doing them with your arm at your side.

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.