21's Bicep Curl (Dumbbell)
21s are a high-volume bicep curl variation that divides the range of motion into three distinct 7-rep segments: bottom-half, top-half, and full-range. This intensity technique maximizes time under tension to build muscular endurance and size.
Because 21s generate significant metabolic stress, AI coaching is crucial for ensuring you select the correct weight relative to your daily recovery status. If your HRV and sleep data indicate high fatigue, the app may recommend regressing to a standard curl to avoid overtraining; conversely, if your readiness is high, it can accurately track RPE to ensure the final 7 reps are truly challenging. The app also learns your endurance capacity over time, adjusting volume to prevent form breakdown during the later stages of the set.
Form Cues
- Stand tall with your core braced and elbows pinned to your sides
- Perform the first 7 reps from the bottom to exactly 90 degrees
- Perform the next 7 reps from 90 degrees to full contraction
- Complete the final 7 reps using a full range of motion
- Squeeze the biceps hard at the top of every repetition
- Don't swing your hips or back to generate momentum
- Don't let your elbows drift forward or backward during the curl
- Don't rest between the three 7-rep segments
- Don't drop the weight quickly; control the lowering phase
Common Mistakes
- Selecting a weight that is too heavy to complete all 21 reps
- Using momentum to swing the weight up
- Resting or pausing between the different segments
- Shortening the range of motion on the final 7 reps
Muscles Worked
This exercise intensely targets both the long and short heads of the biceps brachii by overloading different points in the strength curve. The high repetition count and constant tension also heavily recruit the brachialis and forearm muscles, leading to a significant metabolic pump.
Primary
Secondary
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