The 21s curl is a classic Arnold-era biceps protocol: 7 reps through the bottom half of the curl, then 7 reps through the top half, then 7 full-range reps — 21 reps total without setting the bar down. The combination of partial-range work and accumulated fatigue creates a brutal biceps pump and a serious hypertrophy stimulus.
What it is
The 21s curl is a single set of barbell curls performed in three phases without resting the bar. First, 7 reps from full extension to a 90° elbow angle. Second, 7 reps from 90° to full contraction. Third, 7 full-range reps from extension to full contraction. The set ends at rep 21 — hence the name.
Muscles worked
| Muscle | Contribution |
|---|---|
| Biceps brachii | ~70 % |
| Brachialis | ~20 % |
| Brachioradialis, forearms | ~10 % |
How to 21s curl: 5 steps
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Load light
**Use 50-60 % of standard barbell curl weight.** Grip shoulder-width supinated.
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7 bottom-half reps
**Curl from full extension to 90° elbow angle. 7 reps strict.**
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7 top-half reps
**Without resting, curl from 90° to full contraction. 7 reps strict.**
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7 full-range reps
**Without resting, perform 7 full-range curls.** Bar starts and ends at full extension.
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Set down
**Rest 2-3 minutes** before any further sets. Total: 21 reps.
How it differs from barbell curl
- 21-rep protocol. Three 7-rep blocks at different ranges of motion, no rest in between.
- Partial-range work. Lower and upper halves trained separately for partial-range strength.
- Brutal pump. The continuous tension and high rep count create one of the biggest biceps pumps possible.
- Much lighter loads. Use 50-60 % of your standard barbell curl weight.
Common mistakes
When to use this variation
Use 21s as a biceps finisher after heavy compound curls, in a high-volume arm specialisation phase, or as a pump-focused tool to drive nutrients into the biceps. Program 1-2 sets at end of session. The intensity per set is high — don’t repeat too often.
FAQ
Why three ranges?
The bottom range hits the long head in stretch, the top range hits both heads in peak contraction, and full-range reps integrate the work. Three different stimuli in one set.
What weight to use?
50-60 % of your standard curl 1RM. If you can’t finish all 21 reps, the load is too heavy.
Can I 21s with dumbbells?
Yes — dumbbell 21s work the same way. Most lifters do them with a barbell or EZ-bar for the bilateral pump, but dumbbells are perfectly valid.
Related exercises
- Barbell Curl: standard full-range version
- EZ-Bar Curl: wrist-friendly bar option
- Cheat Curl: another heavy-volume biceps finisher
- Preacher Curl: isolated alternative
