Concentration Curls
Also works: Forearms
Seated with the back of your upper arm braced against your inner thigh, the concentration curl removes every route to cheating: no hip drive, no shoulder swing, no leaning back. The elbow sits ahead of your torso, so the biceps works hardest near full flexion rather than at the bottom.
Own the movement
Set up first, then execute. Every cue below is something you can check on your next set.
Before the first rep
- Sit on the end of a flat bench with your feet flat and wide, knees at roughly 90 degrees.
- Pick the dumbbell up with one hand and plant the back of that upper arm flat against the inside of the same-side thigh, just above the knee.
- Let the arm hang straight down with the palm turned forward, dumbbell just clear of the floor.
- Put your free hand on the other thigh and lean forward slightly from the hips, back flat.
- Choose a weight roughly 30-40% lighter than you use for a standing two-hand curl.
Every rep
Breathing & tempo — Exhale as you curl, inhale on the way down. One second up, one second held at the top, three seconds down — the slow lowering is where most of the work happens at this load.
Sets, reps & load
Where to start, and what to change when it stops being hard.
Start with 6-8 kg. Most people who curl a 15 kg dumbbell standing will need 8-10 kg here once the swing is gone. Add weight only when you can hold a one-second squeeze at the top of every rep in all sets; otherwise add a rep or slow the lowering phase.
What goes wrong
The errors that show up most often, and the cue that fixes each one.
Set your free hand on the opposite thigh and press down into it. If the torso still moves, drop 2-4 kg — you have removed the only reason to do this movement.
Actively press the triceps into the leg for the whole set, as if trying to push your thigh outwards. Keep the contact point above the knee, not near the hip.
Lower until the arm is visibly straight and the dumbbell nearly touches the floor. Count three seconds down so you cannot rush past the bottom.
Use a weight you can control for 10-15 strict reps with a one-second hold. Biceps shape is genetic; only size responds to training, and size comes from total quality reps.
Why bother
Bracing the triceps against the thigh fixes the humerus in place. That is the whole design: with the upper arm physically pinned, the only joint left to move is the elbow, so the load cannot be smuggled onto the front delts or the lower back the way it can on a standing curl.
Because the elbow sits in front of the body, the shoulder is already slightly flexed and the biceps starts partly shortened. Resistance therefore peaks near the top rather than at the halfway point, which makes this a poor choice for heavy work and a good one for finishing a set of arms with strict, felt reps.
Where it fits
Last or second-to-last in an arm session, after the heavy barbell or cable curl has been done. Two or three sets per arm on one or two days a week. Do not try to make it your main biceps builder; the single-arm format doubles the set time and the load ceiling is low.
If this one isn't it
No kit, too hard, or too easy — here's where to go instead.
Same job, different kit
Start here instead
When this gets easy
Asked and answered
Does the concentration curl build the biceps peak?
No. The height of your biceps peak is set by the shape and insertion point of the muscle, which training cannot change. What this movement does well is deliver strict, fully supinated reps with a hard top-end contraction, which adds size. A bigger biceps looks peakier; that is the whole mechanism.
Why can I only use half the weight I curl standing?
Because the standing version lets you use hip drive, torso lean and shoulder flexion. Pinning the upper arm removes all three. The lower number is the honest one — treat it as a separate exercise with its own log, not a failed barbell curl.
Should I do this standing bent over instead of seated?
The standing version, arm hanging free without thigh support, trains the same range but demands you hold the upper arm still yourself. Use the seated braced version when you want maximum strictness, the standing one when a bench is not free.
Is it worth doing if I already do barbell curls?
As a finisher, yes. It fixes side-to-side strength differences that a barbell hides, since each arm has to move its own load with no help. Two or three sets after your main curl is enough; it is not a replacement for loaded two-arm work.