The concentration curl can be an essential addition to your training routine to help build big arms and make your biceps pop, but are you sure you’re even doing the exercise correctly?

For this movement, you shouldn’t settle for anything other than perfect form—especially because it’s such a killer exercise for a key muscle. Let Men’s Health fitness director Ebenezer Samuel, C.S.C.S. and associate fitness editor Brett Williams guide you through the move’s subtleties, saving you from the bad habits that are keeping you from unlocking your fitness potential.

Before you grab a dumbbells, plop down on the bench, and get pumping on those curls, take note that it’s extremely important to pay attention the movement here. Using the proper form is essential to make sure you’re getting the most out of the exercise—particularly because of how common it is for guys to get lazy with the position, especially in regard to elbow placement. Let’s break down everything you need to know.

Men’s Health

Arm to Thigh

Eb says: The most common mistake you see with the concentration curl comes in the initial setup: Many people try to wedge their elbow into their thigh. But doing basically lets you use both knee and elbow as one big fulcrum, essentially making the curl easier and taking tension off the biceps.

Avoid this by wedging your upper arm into your thigh, thinking of driving the meatiest part of your triceps in there. You’ll have to hinge your waist forward a bit more to do this, but you’ll get more out of the entire curl.

Upper Arm Perpendicular

Eb says: Once you’re in this position, you’re responsibility is to maintain this position. Your upper arm should, for the life of each set, be perpendicular to the ground and stay perpendicular.

You’ll be tempted to lean back as you curl, just as you are on nearly every curl. But fight to keep your upper arm perpendicular to the ground the entire time. Watch yourself in a mirror if possible to check technique.

Don’t Overcurl

Eb says: One of the biggest problems guys have with the concentration curl (and any curl, really) is a tendency to chase an arbitrary endpoint. You may think you have to get the dumbbell to touch your shoulder, for example. Don’t do that.

Curl up only as high as you can before you start to feel your triceps losing contact with your thigh. As long as your forearm is higher than parallel to the ground, you’ll be engaging your biceps. If you try to go beyond this point and your elbow starts shifting forward, all you’re doing is taking stress and focus off the biceps.

Want to master even more moves? Check out our entire Form Check series.