1. Not Locking Your Elbows By Your Sides
Even a lot of experienced bodybuilders get this one wrong because they’re trying to go heavy and increase the range of motion. Curls are a single-joint move, but when you pull your elbows away from your sides in an effort to go higher as you raise the weight, they become a multijoint exercise. Because this shifts some of the emphasis to the front delts, they now share the workload with the bi’s. Instead, fix your elbows to your sides and don’t let them travel forward. At the top of the motion, you shouldn’t be looking directly at the bar; rather, the bar should be near the top of your chest.
2. Failing To Extend Your Elbows
This one would be funny if it weren’t committed by so many trainees. Clearly, to flex the biceps you must bend the elbow, so essentially the degree of elbow bend must change by opening and closing over the course of each rep. Curiously, you’ll see guys who instead rock at the waist and lean back as they curl with almost no change in elbow bend. That’s simply not a rep, and your arms won’t grow! Instead, reduce the weight and pay attention: The angle in your elbows should approach 180 degrees at the bottom, where your arms are almost fully extended, and be decidedly less than 90 degrees at the top of each rep.
3. Dropping Your Elbows From Parallel
When doing high-pulley cable curls, it seems simple enough: Do a double biceps pose by bringing your fists toward the back of your ears. But it’s more complicated when you have a heavy weight pulling against each arm. The tendency here is to drop your arms as your elbows pull forward. Again, this turns an isolation exercise into an unwanted multijoint move. Keep your upper arms locked in a position parallel to the floor so that the only movement occurs at the elbow joints. This effectively makes the short (inner) head do the brunt of the work.
4. Ignoring Overhand and Neutral-Grip Moves
While grabbing a weight and curling it seems elementary for big biceps development, not all the major arm flexors are optimally worked when you use an underhand grip. In fact, when your hands are in the neutral (hammer) or overhand (reverse grip) positions, the brachialis that lies underneath the biceps and brachioradialis — the forearm muscle nearest the elbow — kick into gear. You won’t reach your genetic potential unless you include moves that target all the muscles in the biceps group. We suggest doing one of these exercises last in your biceps workout because it can adversely affect grip strength.
5. Always Using the Same Grip Width
Chances are the standing barbell or EZ-bar curl is the major mass-building movement in your routine, and rightly so. Because you can load up the bar and generate a bit of body english, you can move more weight than with any other biceps exercise. But that doesn’t mean you can’t add some variety to work the target muscles in slightly different ways from time to time. Changing your grip width on barbell curls affects the amount of rotation in your arms. When you use a wider than shoulder-width grip, your arms turn out at the shoulder joints — called external rotation — which hits the short (inner) head more strongly. When you grasp the bar with a narrower than shoulder-width grip, your arms instead turn in — known as internal rotation — and you’ll activate the outer (long) head to a greater degree.