Are 21s better for muscle growth than regular curls?

Not necessarily. 21s have not been compared directly with straight sets of curls, so treat them as a way to add hard, high-rep biceps work and some variety with light dumbbells. The total number of hard sets you do each week matters more than the rep scheme.

Which half of the curl matters more?

The bottom half deserves the most care. In an eight-week study of untrained young women on seated dumbbell preacher curls, the arm trained only through the bottom half of the range gained more full-range strength (about 43% against 19%) and more biceps size near the elbow than the arm trained only through the top half. A preacher curl loads that stretched range harder than a standing curl, so this is no direct test of 21s, but it is a good reason to lower all the way to straight arms on every bottom-half rep.

How heavy should Dumbbell 21s be?

Noticeably lighter than the dumbbells you use for a normal set of 10 to 12 curls, light enough that the last full-range reps are still strict. If you have to swing to finish, go lighter on the next set.

How many sets of 21s should I do?

One to three sets at the end of an arm or pulling session is typical, with 1 to 2 minutes of rest between sets. Count them toward your weekly biceps volume rather than adding them on top of a full curl workout.

Should I curl both dumbbells together or alternate arms?

Both work, but curling them together, as shown here, keeps the set continuous and makes it easier to stop both arms at the same halfway point. Alternating gives each arm a short pause while the other works, so the set takes longer and feels a little easier.

Can I do 21s with a bar instead?

Yes. EZ Bar 21s use the same seven-rep split with an angled bar, which many lifters find easier on the wrists than a straight Barbell Curl grip.

Dumbbell 21s

What Are Dumbbell 21s?

Dumbbell 21s are an isolation exercise that primarily targets the biceps and also engages the brachialis, brachioradialis and forearm flexors. They are an intermediate-level movement that turns one set of standing dumbbell curls into 21 reps, with seven through the bottom half of the curl, seven through the top half and seven through the full range, and no rest between the three parts.

The method is a long-standing bodybuilding technique for keeping the elbow flexors under tension for one long, continuous set. It produces a strong pump and plenty of fatigue with light dumbbells, which is why it is usually programmed as a finisher, one to three sets at the end of an arm or pulling session after the heavier curl work is done.

The halfway point, with the forearms parallel to the floor, is where a standing curl is hardest, and both partial ranges pass through it. Dumbbells let each arm work on its own, so a stronger side cannot carry a weaker one, and holding the palms fully turned up keeps the forearm in the position where the biceps pulls hardest. The same scheme done with an angled bar is EZ Bar 21s.

Dumbbell 21s suit lifters who can already perform a strict Dumbbell Curl without swinging. If that is still a challenge, build up with straight sets of regular curls first, or shorten each part to five reps until all three ranges stay controlled. Paying attention to the exact halfway point matters more here than in most curls, because it is what separates the two partial ranges.

Muscles Worked

MuscleActivation

Biceps Brachii: Primary
Brachialis: High
Brachioradialis: Medium
Deltoid: Low
Flexor Carpi Radialis: Low
Flexor Carpi Ulnaris: Low

Instructions

Stand with your feet about hip-width apart and hold a dumbbell in each hand with an underhand grip, palms facing forward.
Let the dumbbells hang at arm's length beside your thighs with your elbows close to your sides, chest up and core braced.
For the bottom half, curl both dumbbells together until your forearms are parallel to the floor, then lower them under control until your arms are straight. Do 7 reps.
On the 7th rep, stop with your forearms parallel to the floor instead of lowering the dumbbells.
For the top half, curl the dumbbells from that halfway point up to the front of your shoulders, squeeze your biceps, and lower only back to the halfway point. Do 7 reps.
After the 7th top-half rep, lower the dumbbells all the way to straight arms.
For the full range, curl from straight arms to the front of your shoulders and lower back to straight arms. Do 7 reps.
Keep your palms facing up, your upper arms still and your torso upright for all 21 reps. Exhale as you curl and inhale as you lower.
Set the dumbbells down after rep 21 and rest before the next set.

Common Mistakes

Going too heavy
Dumbbells that suit a normal set of curls turn the last full-range reps into swings, so pick a weight you can control for all 21.
Swinging the torso
Rocking the hips or leaning back moves the dumbbells with momentum, taking work off the biceps and loading the lower back.
Losing the halfway point
Letting the stopping point drift above or below forearms-parallel blurs the bottom-half and top-half ranges into the same reps.
Elbows drifting forward
Pushing the elbows forward on the top-half reps hands part of the work to the front of the shoulders and lets the biceps rest at the top.
Letting the palms turn in
Rotating the dumbbells toward a hammer grip as fatigue builds takes the biceps out of its strongest position, so keep the palms facing up throughout.
Resting between parts
Pausing or setting the dumbbells down between the three ranges breaks the continuous set that gives 21s their effect.

Injuries

Dumbbell 21s are a low risk exercise when performed with proper technique. The elbow tendons and wrists take most of the strain, because the long continuous set keeps the elbow flexors working far longer than a normal set of curls. Frequent or high-volume use can irritate the front or inside of the elbow, and leaning back to finish the last full-range reps loads the lower back.

The most serious risk, though rare, is a tear of the biceps tendon at the elbow, most often when the dumbbells are too heavy and are allowed to drop so the elbows snap straight under load. Choose dumbbells noticeably lighter than your usual curl weight, warm up with a set of regular curls, keep 21s to one to three sets near the end of a session, and lower every rep under control.

If you cannot finish all 21 reps without swinging, cut each part to five reps or return to straight sets of Dumbbell Curl or Machine Bicep Curl. If holding the palms fully turned up bothers your wrists or elbows, Dumbbell Hammer Curl keeps a neutral grip. Once all 21 reps feel controlled, progress by adding a small amount of weight or slowing the lowering phase rather than adding more sets.

Stop immediately if you feel a sudden pop at the front of the elbow, sharp pain or sudden weakness, and see a doctor if swelling, bruising or a bulge in the upper arm follows. A burning pump by the last reps is normal, but joint pain is not.

Overview

Primary Focus: Biceps
Equipment: Dumbbell
Modality: Strength
Difficulty: Intermediate

Alternative Exercises

Frequently Asked Questions

Q: Are 21s better for muscle growth than regular curls?: Not necessarily. 21s have not been compared directly with straight sets of curls, so treat them as a way to add hard, high-rep biceps work and some variety with light dumbbells. The total number of hard sets you do each week matters more than the rep scheme.
Q: Which half of the curl matters more?: The bottom half deserves the most care. In an eight-week study of untrained young women on seated dumbbell preacher curls, the arm trained only through the bottom half of the range gained more full-range strength (about 43% against 19%) and more biceps size near the elbow than the arm trained only through the top half. A preacher curl loads that stretched range harder than a standing curl, so this is no direct test of 21s, but it is a good reason to lower all the way to straight arms on every bottom-half rep.
Q: How heavy should Dumbbell 21s be?: Noticeably lighter than the dumbbells you use for a normal set of 10 to 12 curls, light enough that the last full-range reps are still strict. If you have to swing to finish, go lighter on the next set.
Q: How many sets of 21s should I do?: One to three sets at the end of an arm or pulling session is typical, with 1 to 2 minutes of rest between sets. Count them toward your weekly biceps volume rather than adding them on top of a full curl workout.
Q: Should I curl both dumbbells together or alternate arms?: Both work, but curling them together, as shown here, keeps the set continuous and makes it easier to stop both arms at the same halfway point. Alternating gives each arm a short pause while the other works, so the set takes longer and feels a little easier.
Q: Can I do 21s with a bar instead?: Yes. EZ Bar 21s use the same seven-rep split with an angled bar, which many lifters find easier on the wrists than a straight Barbell Curl grip.