Exercise library
Bicep Curl
Why the elbow position decides everything, how supination adds contraction, and the three curl variations that cover the whole muscle.
How to do the bicep curl
- 01Stand tall with a dumbbell in each hand, arms straight, palms facing forward.
- 02Squeeze your glutes and brace your midsection so your torso cannot swing.
- 03Keep your elbows pinned at your sides and curl the weights up by bending only at the elbow.
- 04At the top, squeeze without letting the elbows travel forward — the forearm should stop before vertical.
- 05Lower over three seconds to fully straight arms. The bottom stretch is part of the rep.
Coaching cues
- Elbows stay at your ribs. If they move forward, the front delts took over.
- Turn your little finger toward the ceiling at the top to fully supinate.
- Straighten completely at the bottom — partial curls build partial arms.
Common mistakes
FaultSwinging the torso to start each rep
FixBrace and squeeze the glutes, or curl with your back against a wall. If you still need momentum, the weight is too heavy.
FaultElbows drifting forward at the top
FixThat brings the front delts in and unloads the biceps at exactly the point you were trying to contract them.
FaultNot straightening at the bottom
FixThe stretched position is where a lot of the growth stimulus lives. Full extension every rep.
FaultOnly ever doing standing curls
FixAdd an incline curl for the stretched position and a preacher or spider curl for the shortened one.
Arm training is where good lifters abandon their own standards. The curl is a single-joint movement with one rule, and most people break it on rep one.
The elbow does not move
Your upper arm stays vertical and pinned to your side. The forearm rotates around the elbow. That is the entire exercise.
When the elbow drifts forward at the top, the front deltoid takes over and lifts the weight through the last third of the range — precisely where you were trying to contract the biceps hardest. The rep looks complete and the muscle did less.
A useful test: curl with your back and elbows against a wall. If the weight suddenly feels much heavier, momentum and shoulder drift were doing more than you thought.
Supination is half the job
The biceps do two things: they bend the elbow and they turn the palm upward.
A barbell fixes your hands, so only the first function is trained. With dumbbells you can start with a neutral grip and rotate as you curl, finishing with the little finger turned slightly toward the ceiling. That trains the muscle in both of its roles and is the main reason dumbbells belong in arm training.
Use the whole range
Full extension at the bottom, under control, on every rep.
The lengthened position is where a disproportionate share of the growth stimulus sits, and it is the first thing people cut when the set gets hard. Three seconds down and a complete straighten does more for arm size than another five kilos.
Cover the positions
The biceps cross the shoulder as well as the elbow, so arm position changes which part of the range is loaded hardest.
Incline curls, with the arms hanging behind the body, load the stretched position. Preacher or spider curls load the shortened one. Standing curls sit in the middle. Two of the three, rotated over a training block, covers the muscle far better than three sets of the same standing curl forever.
Remember the biceps also work in every pull-up and row you do — direct curl volume is added on top of that, not instead of it.
Common questions
Why are my biceps not growing from curls?
Usually momentum and partial range. If your torso swings and you never fully straighten your arms, the biceps are doing a fraction of the work at a fraction of the range. Lighter weight, strict elbows and a full lockout at the bottom fixes most stalled arm training.
Should I fully straighten my arms between reps?
Yes. The stretched position under load is a significant part of the growth stimulus, and stopping short to keep constant tension removes it. Control the lowering rather than shortening the range.
Dumbbells, barbell or cable for curls?
Dumbbells allow supination and let each arm work independently. A barbell allows the most load but fixes your wrists. Cables keep tension constant through the range. Rotate between them rather than searching for the best one.
What does supination do in a curl?
The biceps both flex the elbow and supinate the forearm — turning the palm upward. Deliberately rotating your little finger toward the ceiling as you curl recruits the muscle in both of its functions, which a fixed barbell grip cannot do.
How many sets of curls should I do?
Six to ten hard sets a week is plenty for most people, spread over two sessions. The biceps also work in every row and pull-up you do, so direct curl volume sits on top of an already meaningful workload.
Swap it out
Same training effect, different demand on the joints.