Bicep 21s: A Complete Guide | Form, Benefits, and Alternatives!

By
Mike Kenler
October 23, 2020

Bicep 21s

Bicep 21s, also known as the 21s bicep curl, fully activate both your biceps and forearms. This compound exercise will test the strength and endurance of your biceps. So if you want to improve your arm size, strength, and aesthetics, bicep 21s are for you! 

Muscles Worked by Bicep 21s

Primary Muscle Groups:

Bicep 21s primarily work your biceps brachii. The bicep muscle is comprised of two “heads:” a long head and a short head. Both heads work together as a cohesive unit during lifting and pulling motions.

The 21s bicep curl also primarily targets the brachioradialis, one of the strongest and most visible muscles in the forearms. The main functions of the brachioradialis are forearm flexion, supination and pronation. 

Secondary Muscle Groups:

Bicep 21s secondarily work your brachialis, a muscle in your biceps that lies beneath your biceps brachii. This exercise also works your abs and back muscles, as they activate to stabilize your body during the curling motion. Other smaller forearms muscles are also worked during the 21s bicep curl.

Bicep 21s Benefits

1. Strength and Size Gains

The 21s bicep curl is a powerful compound bicep exercise. Compared to standard bicep curls, bicep 21s maximize time under tension during the exercise motion. As a result, the increased time under tension strengthens the biceps muscle and increase biceps hypertrophy.

Growing your biceps isn’t just for show — it will improve your performance in other exercises at the gym such as the barbell row and the lat pulldown

2. Forearm Activation

Bicep 21s offer the benefits of two exercises in one, as they work the biceps and the forearms simultaneously. During the 21s bicep curl, your forearms continuously activate to support your arms during each phase of the lift. In that way, you can benefit from working your upper and lower arms at the same time. 

3. Improved Aesthetics

Let’s face it — nearly everyone wants to have better looking arms. Depending on your goals, you can use bicep 21s to develop bigger, more toned, or more defined biceps and forearms. Although this is an intense exercise, it is relatively simple to learn and can help you improve the appearance of your arms in no time. 

How to Do The Bicep 21s

Equipment:

For this exercise, you will need a pair of dumbbells, a barbell, an EZ bar, or another form of resistance to curl.

Setup:

1. Grab your preferred form of resistance with a supinated underhand grip.

2. Assume a standing position in a comfortable stance with your hands by your sides.

Action:

Part 1

1. Keeping your back straight, engage your core and contract your biceps to curl upwards halfway until your hands are in line with your elbows.

2. Pause for a moment and return to the starting position. Repeat this half curl six more times for a total of seven reps.

Part 2

3. Starting from a half-curl position with your hands in line with your elbows, contract your biceps to curl upwards until your hands are near your shoulders.

4. Squeeze your biceps hard at the top and return to the starting position. Repeat this half curl six more times for a total of seven reps.

Part 3

5. Lastly, bring your hands back down by your sides and contract your biceps to curl all the way upwards until your hands are near your shoulders.

6. Squeeze your biceps hard at the top and return to the starting position. Repeat this full bicep curl six more times for a total of seven reps.

7. You have now completed the bicep 21! Repeat this process for your desired number of sets.

Recommendation:

If you are new to the 21s bicep curl, choose a light weight to begin. You can use the bicep 21s as a one time finisher for your bicep workout or complete the 3-4 sets of the bicep 21s for a complete exercise circuit. 

Bicep 21s Mistakes

1. Rounding the Back

Many weightlifters tend to round their back during the 21s bicep curl. This rounded back position most often happens when fatigue sets in towards the end of the exercise. A rounded back compromises the safety of your spine and can easily lead to injury.

Instead, choose a lighter weight and make sure your back is engaged in order to challenge your biceps in the safest way possible. 

2. Using Momentum

Far too often, people tend to swing their arms and use momentum to lift the weight up during bicep 21s. Usually, this happens because they try to lift too much weight.

Instead of allowing ego to get in the way, choose a lighter weight and focus on perfecting your form. Being mindful while lifting lighter weight will actually increase your gains and reduce your chances of injury!

3. Rushing the Motion

Another common mistake made during the 21s bicep curl is rushing. In other words, people explode through the curl and then let the dumbbells fall quickly to the bottom to "make it through" the exercise motion. This mistake steals major gains that can be made during the eccentric portion of the exercise motion.

Instead of rushing through the motion, curl up and down in a slow, controlled fashion. Not only is this safer, but it will increase your time under tension and maximize the benefits of bicep 21s.

Bicep 21s Variations

1. Reverse Straight Bicep 21s

The reverse 21s bicep curl targets your forearms more than traditional bicep 21s. Begin in the same setup position as the original, but curl upwards with your palms facing down. Other than this change, the form remains the same!

 


2. Dumbbell Hammer Grip Bicep 21s

Compared to standard bicep 21s, the hammer grip variation of the 21s bicep curl better activates the brachialis muscle in your upper arm. Begin in the same setup position as the original, but curl the dumbbells upwards with your palms facing each other with a neutral grip. Complete the bicep 21s with the same form as the original.

3. Straight Bar Bicep 21s

You can also complete the bicep 21s with a cable machine. Assume a standing position in front of a cable machine and set the straight bar attachment at the lowest setting. Grab the straight bar with an underhand grip. Engage your core as you carry out the 21s bicep curl with the same form as the dumbbell, barbell, or EZ bar variation. Repeat!

Bicep 21s Alternatives

If you enjoyed the bicep 21s, check out these alternative exercises to improve your bicep training:

1. Dumbbell Zottman Curl 

Grab a pair of dumbbells with your palms facing forward. Assume a standing position with your feet roughly hip width apart.

Keeping your back straight, contract your biceps to curl the dumbbells upwards. Squeeze your biceps hard at the top and twist your hands so that your palms face downwards.

Slowly lower the dumbbells to the starting position and twist your hands so that your palms are facing forward again. Repeat!


2. 1-Arm Kettlebell Regular Curl

Assume a comfortable standing position with your back straight. Grab a kettlebell with your right hand and your palm facing forward. Contract your right bicep to curl the kettlebell upwards. Squeeze your bicep hard at the top of the rep and slowly return to the starting position.

Repeat for your desired number of reps and switch to the left arm!


3. Barbell Close Curl 

Assume a comfortable standing position with your back straight. Grab a barbell with a double supinated grip and your hands close together. Contract your biceps to curl the barbell upwards.

Squeeze your biceps at the top and slowly return to the starting position. Repeat!


Looking for an Intense Bicep Workout?

Follow along to this 5-minute dumbbell bicep workout!

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Mike Kenler
Director of Writing | Certified in Plant Based Nutrition at T. Colin Campbell Center for Nutrition Studies

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