Whether you do preacher curls with a cable machine (harder when your arm is bent) or a barbell (harder when your arm is straight), your biceps grow about the same amount after 10 weeks of training.

Whether you use a cable machine or a barbell to do preacher curls for 10 weeks, your biceps will grow about the same amount — the exact way you apply resistance doesn’t matter much for muscle size.

Doing preacher curls 3 times a week for 10 weeks makes your biceps bigger and stronger, no matter if the exercise feels hardest when your arm is straight or bent.

When you do preacher curls for 10 weeks, your strength in the middle and fully bent positions gets better no matter if you use a cable or barbell — the resistance pattern doesn’t make a difference there.

If you do preacher curls with a barbell (harder when your arm is straight), you get stronger at keeping your arm slightly bent than if you use a cable machine (harder when your arm is fully bent).

If you do preacher curls with a barbell — where it’s hardest when your arm is almost straight — you’ll get stronger specifically at that position better than if you use a cable machine where it’s hardest when your arm is bent.