Concentration curl: the seated setup, where the rep is hard, and how it compares with other curls

A concentration curl is a one-arm dumbbell curl done seated, leaning forward, with the back of your upper arm braced against the inside of your thigh. The brace stops your upper arm and your body from helping, so the muscles that bend the elbow do the lifting: the biceps, the brachialis underneath it, and the brachioradialis along the thumb side of the forearm.

This page covers the setup, where the rep is hardest, what the research says about training one arm at a time and about feeling the squeeze, how the concentration curl compares with the preacher curl and the standing curl, the faults, and the sets. How curls fit next to your rows, and how much direct arm work a week needs, is on the arm workout.

How to do a concentration curl

1. Sit on the end of a flat bench, feet wider than your hips and flat on the floor.
2. Take a dumbbell in one hand, palm facing away from your thigh, and lean forward from the hips.
3. Brace the back of that upper arm against the inside of the same thigh, just above the knee, so the arm hangs straight down with the dumbbell near the floor. Rest your other hand on your other thigh.
4. Curl the dumbbell up toward the front of your shoulder, keeping your upper arm pressed to your thigh.
5. Stop when your forearm is close to vertical, just before the dumbbell would rest over your elbow.
6. Lower it under control, taking about two seconds, until your arm is straight. That's one rep. Finish the set, then switch arms.

Where the rep is hard

A dumbbell is hardest to curl when your forearm is level with the floor and easiest when your forearm points straight down or straight up. With your upper arm hanging straight down, that puts the hard part of a concentration curl in the middle of the rep, about where your elbow is bent at a right angle. The bottom, with your arm straight, is light, and so is the top.

That's the difference from the preacher curl, where the sloped pad holds your upper arm out in front of you and moves the hard part toward the bottom. In 22 people doing one light rep of each of three dumbbell curls, the preacher curl's biceps activity peaked at the start of the lift and stayed high over only a short part of the range, while the incline curl and the plain dumbbell curl kept it high throughout.¹ The concentration curl wasn't one of the three; no study found for this page measured it the same way.

One arm at a time

A concentration curl trains one arm while the other rests. A 2025 meta-analysis of nine studies compared training one limb at a time with training both together: muscle growth didn't differ significantly, two-limb training raised two-limb strength more, and one-limb training raised one-limb strength more.² So working one arm at a time is a choice of convenience and focus, not a growth advantage.

Two practical notes. Start each set with your weaker arm and match its reps with the other, and expect a one-arm set to take about twice as long as a two-arm set of the same reps.

Feeling the squeeze

Many lifters judge the concentration curl by how strongly they feel the biceps work. That feeling may not match what the muscle is doing. In 13 male soccer players with lifting experience, who rated how hard each target muscle worked after six upper-body exercises, the concentration curl among them, and then had their muscle activity measured, the ratings didn't correlate significantly with the measured activity in any of the six exercises.³

So aim at what you can count: a full range, a controlled lowering, and reps that end one or two short of failure. Whether thinking about the muscle changes the result is a separate question, covered on the mind-muscle connection.

Concentration curl vs preacher curl and the standing curl

No trial found for this page has compared the concentration curl with another curl for growth or strength; a PubMed search turned up four records that used it, none of them that comparison. What a trial has shown is that a curl itself does the job. In 10 untrained men who trained one arm with a one-arm curl and the other with a one-arm dumbbell row for eight weeks, the curl arm's elbow flexors grew 11.06% and the row arm's 5.16%.⁴ That was a curl, not the concentration curl, so read it as support for curls in general. Pick the curl you can do with a full range and add weight to over time. The thumbs-up grip is on hammer curls.

The common faults, and a fix for each

• Lifting the elbow off your thigh. Your shoulder takes over the top of the rep. Keep the back of your upper arm pressed to your thigh the whole set.
• Leaning back to finish the rep. Stay leaning forward; if you need your back to get the dumbbell up, it's too heavy.
• Stopping short at the bottom. Lower until your arm is straight. The bottom is the light part, so skipping it saves little effort and costs range.
• Curling past vertical. Once the dumbbell is over your elbow, the arm muscles rest. Stop just before.
• Dropping the weight. Lower it in about two seconds; the way down is half the rep.
• Pulling through something that hurts. Sore muscles the next day are normal; a sharp or lasting hurt in the elbow or the arm isn't. Stop, and see a doctor or a physical therapist.

Sets, reps and where it goes

• Two or three sets of 10 to 15 per arm near the end of an upper-body or pull day, stopping one or two reps short. (How to judge reps left.) The American College of Sports Medicine's 2026 position stand, which covers healthy adults, advises at least two sets per exercise.⁵
• Count it with your other curls. The same stand found muscle growth was enhanced by ten or more sets per muscle group a week. Your rows and pull-ups work the biceps too; the arm workout shows how to count them.
• Use it as the second curl after a two-arm curl, or as the only curl when all you have is a bench and one dumbbell.
• Add weight in small steps. When 15 reps come easy on both arms, go up by the smallest jump you have. (Progressive overload covers the options.)

If you'd rather not plan it alone

The concentration curl is one exercise; deciding how many curls your week needs next to your rows and pull-ups, and when to change them, is the part a page can't do. Coaching is the version where your workouts are built around the days you actually have, and a weekly call looks at the week you just had and rebuilds the next one. Coaching to build muscle explains how that works, and here's how to apply. Otherwise: at your next upper-body session, try two sets of 12 concentration curls per arm, weaker arm first, and write down the weight.