21's Bicep Curls Workout (Proper Form & Benefits)

Connor Sellers
Published by Connor Sellers | Senior Coach
Last updated: April 2, 2024
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If you've reached a plateau in your bicep training with standard bicep curls, incorporating 21s bicep curls can inject fresh energy into your arm workouts.

Made famous by Arnold Schwarzenegger, this training system increases the biceps' strength and hypertrophy by maximizing the time under tension during the exercise.

Being a personal trainer, I constantly explore diverse training methods to create highly effective workout routines for my clients.

After conducting extensive research and using training for several weeks, I've decided to share a comprehensive guide on multiple biceps 21s variations, proper form techniques, and common mistakes to avoid to maximize your results.

Quick Summary

  • The 21 biceps curls may help you increase hypertrophy, improve strength, prevent plateaus, enhance muscle and mind connection, and promote physical appearance.
  • The 21s bicep curls variations include 21s concentration curls, 21s hammer curls, reverse straight bicep 21s, 21s preacher biceps, and 21s standing biceps cable curls.
  • Research findings published by Ovid have consistently shown that generating muscle tension through a partial range of motion exercises can effectively stimulate muscle hypertrophy
  • In my opinion, bicep curls 21s offer a unique and effective way to challenge your muscles, overcome plateaus, and achieve a more sculpted appearance, making them a valuable addition to any workout routine.

How to Do Bicep Curls 21s?

Person doing a bicep curl

Based on my first-hand experience, here's how you can perform dumbbell 21s bicep curls:

  1. Stand shoulder-width apart while holding two dumbbells by the sides of your thighs with your palms facing up.
  2. Contract your biceps to curl upwards halfway until your hands align with your elbows. When you do this exercise, engage your core and keep your back straight.
  3. Take a brief pause of two to three seconds before resuming back to the initial position.
  4. Repeat this half curl until you complete seven reps.
  5. Curl the weight upwards to your biceps near the shoulder level from where your hands are in line with your elbows.
  6. Pause while squeezing your biceps at the movement's top and return to the starting position. Repeat until you complete seven reps.
  7. Return the dumbbells to the sides of your thighs and raise them until your hands are near your shoulders.
  8. Pause while squeezing your biceps at the movement's top before returning to the starting position.
  9. Repeat until you complete the last seven reps.

“Don’t recruit the shoulders or torso to swing the weights up when doing the dumbbell curl. This can feel like a swinging, twisting, or heaving movement. Do not allow your hips to hinge or your lower body to assist the movement in any way.”

- Paul Rogers, Personal Trainer

What Are the Variations of Biceps 21s?

Variation of a bicep curl

The variations of 21s bicep curls are the 21s concentration curls, 21s hammer curls, reverse straight bicep 21s, 21s preacher biceps, and 21s standing biceps cable curls. These are effective ways to build overall arm strength and increase bicep size.

1. Concentration Curls 21s

To perform the concentration curls 21s:

  1. Sit on the edge of a bench with your feet flat on the ground.
  2. Grab a dumbbell between your legs with one hand using an underhand grip.
  3. Lean forward, then position your active upper arm against your thigh.
  4. Raise the dumbbell until your elbow reaches a 90-degree angle.
  5. Lower the weight back down to the starting position.
  6. Repeat this motion until you complete seven reps.
  7. Maintain the 90-degree angle at the elbow position once you complete the seventh curl.
  8. From this position, curl the weight upward, bringing the dumbbell to a point approximately one to two inches away from your shoulder.
  9. Lower the weight back to the 90-degree elbow position and repeat for seven reps.
  10. Return your arms to full extension.
  11. Perform seven reps of full-range motion curls, curling the weight to full contraction approximately one to two inches from your shoulder.

2. Hammer Curl 21s

To perform the hammer curl 21s, follow similar steps as the 21s standard biceps curl, except for the grip. Instead, use a neutral grip.

You have the flexibility to do the hammer curl 21s with dumbbells, resistance bands, or a cable machine.

3. Reverse Straight Dumbbell Curl 21s

Person doing a bicep curl

To perform the reverse straight dumbbell curl 21s, start with the same setup position as the standard biceps curls.

However, instead of curling with your palms facing up, curl upwards with your palms facing down.

The rest of the form remains unchanged, including maintaining proper posture and controlled movements throughout the exercise.

4. 21s Preacher Biceps

To do this exercise using dumbbells, follow the same steps as bicep curls but slightly modify the grip. Instead of a palms-forward grip, use an underhand grip. You can do preacher curls using various equipment options, such as the preacher curl machine, EZ curl bar, dumbbells, or a high-quality cable machine.

“To get the best out of this exercise, your upper arms and chest need to be glued to the pad at all times. So, take the time to adjust the pads to make this happen. Being too low or too high will put you out of position and it will be difficult to keep your body against the pad.”

- Garett Reid

What Are the Benefits of Biceps 21s?

Person doing a bicep curl

My findings show that biceps 21s offer a range of benefits, including increased hypertrophy, improved strength, the ability to overcome plateaus, enhanced muscle-mind connection, and a more sculpted physical appearance.

Increase Hypertrophy

Research findings published by Ovid have consistently shown that generating muscle tension through a partial range of motion exercises can effectively stimulate muscle hypertrophy [1].

According to a study published by the National Institutes of Health (NIH), integrating 21s bicep curls into your workout regimen can help you increase muscle mass in your biceps brachii, composed of brachioradialis (responsible for supination, pronation, and forearm flexion), and brachialis (which produces the majority of force during elbow flexion), by prolonging the Time Under Tension (TUT) and inducing a more significant metabolic stress response [2].

Related: Best Hypertrophy Program

Enhanced Strength

Incorporating biceps 21s into your training regimen contributes to developing stronger biceps muscle and overall upper and lower arms, improved grip strength, and enhanced upper body strength.

Prevent Plateaus

Person doing a bicep curl

Incorporating the 21s bicep curls in your upper body workout routine can be an excellent strategy to challenge your muscles if you find yourself stuck on a plateau.

This training system creates significant tension on the targeted muscles, pushing your body to new limits and forcing your biceps to adapt and respond to the increased demands, potentially breaking through plateaus and stimulating further progress.

“If you lift weights, alter your routine by doing fewer reps with heavier weights and vice versa. You can also do a drop set to increase muscle growth and muscular endurance. The technique involves lifting a weight load to failure and then reducing the load for each of the following sets.”

- Emily Cronkleton, Fitness Expert

Improve Your Mind Muscle Connection

You can amplify your mind-muscle connection by slowing the movements, emphasizing on the contraction, and maintaining proper form.

As per findings from ScienceDirect, this deliberate emphasis has demonstrated its ability to support the establishment of efficient movement patterns, ultimately enhancing coordination and exercise control [3].

Add Variety to Your Workout

Person doing a bicep curl

Incorporating biceps curls 21s into your workouts is an excellent strategy to introduce variety to your biceps training.

By utilizing this method, you can effectively overcome training plateaus, prevent boredom, and elevate the intensity of your workouts.

Improved Physical Performance

In addition to sculpting bigger, more defined biceps and forearms, the benefits of growing your biceps extend beyond mere aesthetics.

Developing your biceps can significantly enhance your performance in other gym exercises.

Common Biceps 21s Mistakes

People doing bicep curls
  • Using momentum - Refrain from swinging your arms and relying on momentum to move the weights when performing this bicep workout. Maintaining constant tension on your muscles throughout the entire range of motion is essential to fully reap the benefits and achieve the intended purpose of the exercise.
  • Using heavy weights - Building upon the previous point, it is advisable to select light to moderate weights for this bicep exercise. If you opt for excessively heavy weights, you may find yourself resorting to swinging the weights rather than engaging the targeted muscles.
  • Rushing the last reps - It is important to resist the temptation of rushing through the last seven reps of the exercise, especially when you begin to feel a significant burning sensation in your bicep muscle. It is crucial to lift and lower the weight in a slow and controlled manner to maximize muscle tension and metabolic stress.
  • Rounding the back - As fatigue sets in during the last reps, be cautious of rounding your back. Stay aware of your spine's alignment as you transition between reps. Opting for lighter weight and ensuring the proper engagement of your back muscles will help you challenge your biceps safely and effectively.
  • Not changing equipment or weights - It is crucial to keep challenging your muscles to prevent your body from adapting to the same training stimuli. There are various ways to achieve this, such as altering the equipment used, changing sets and reps, incorporating different training methods, experimenting with grip variations, and even changing up your body positioning and angle.


What are Biceps 21s?

Biceps 21s are bicep curls divided into three ranges of motions. Within this bicep exercise, you perform seven partial reps at the bottom half, followed by seven reps targeting the top half of the movement, and seven more reps of full biceps curls. This exercise is intended to increase the time under tension and, as a result, increase biceps strength and hypertrophy.

What Are the Muscles Worked By 21s Bicep Curls?

The muscles worked by bicep 21s are the biceps brachii muscles, which consist of two heads: the brachialis, and brachioradialis. These muscles are responsible for elbow flexion and forearm rotation. The 21s bicep curls also work the forearms to a lesser extent.


  1. https://oce.ovid.com/article/00124278-201905000-00016/HTML
  2. https://pubmed.ncbi.nlm.nih.gov/20847704/
  3. https://www.sciencedirect.com/science/article/abs/pii/S0167945709001201
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About The Author

Senior Coach
Connor Sellers holds a degree in Kinesiology and Exercise Science from Rutgers University He is an author and personal trainer with the mission to inspire people to relentlessly pursue their fitness and lifestyle goals. He mantra is that staying fit has an overall positive effect on one’s body, mind, and spirit.
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Dr. Harshi Dhingra, MBBS, MD is a published peer-reviewed author and renowned physician from India with over a decade of experience. With her MBBS from Bharati Vidyapeeth and an MD from Rajiv Gandhi University, she actively ensures the accuracy of online dietary supplement and medical information by reviewing and fact-checking health publications.
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Dr. Kristy June Dayanan, BS, MD is an author with a BS degree from University of the Philippines and an MD from University of Perpetual Help System. Her ability to simplify medical science complexities and dietary supplement jargon for the average reader makes her a valued medical fact checker and reviewer.
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