If you're someone who works out regularly, doing certain types of arm exercises—especially those that stretch the muscle while lifting—can noticeably boost your strength. Both fully stretched and mixed-range workouts seem to help about the same.

For people who work out regularly, doing bicep curls with the muscle stretched versus using a mix of stretch and squeeze doesn’t really make a difference in strength gains when lifting in the shortened position.

If you're new to lifting and do cable curls the same way each time, it doesn't really matter whether your arms are stretched far back or in a neutral position — your biceps will grow about the same amount after 10 weeks.

If you're a young guy just starting out, doing bicep curls with your arms in front of you or behind you gives about the same strength gains after 10 weeks — even if one seems to improve a bit more, the difference isn’t really meaningful.

If new gym guys do a specific arm curl workout for 10 weeks — going until their muscles are totally tired — their biceps get about 7% to 9% thicker, no matter how their shoulders are positioned, as long as the movement and resistance stay the same.

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.