21s

Which muscles does it train?

Equipment needed

How to perform it

Isolation work is usually trained in a higher rep range: 2 to 4 sets of 10 to 15 reps with 45 to 90 seconds of rest, performed under control.

Execution and technique cues

• Grip the barbell shoulder-width with a supinated grip, stand tall with a soft knee bend, and pin the elbows firmly against the sides of the torso.
• Perform the first 7 reps through only the bottom half of the range of motion, from full extension up to the point where the forearms are parallel to the floor.
• Without resting, perform the next 7 reps through only the top half, from the parallel position up to full bicep contraction at the top.
• Complete the set with 7 full-range reps, maintaining strict upright posture and fixed elbow position throughout all 21 repetitions.

Common mistakes

• Swinging the torso backward to generate momentum, which shifts load off the biceps and puts unnecessary stress on the lower back.
• Letting the elbows drift forward at the top of the movement, which reduces peak bicep tension and shortens the effective range of contraction.
• Choosing too much weight so that form deteriorates during the final 7 full-range reps, defeating the purpose of the accumulated fatigue.

Frequently asked questions

What is the correct sequence for 21s?

Start with 7 reps from full extension to the midpoint (forearms parallel), then immediately do 7 reps from the midpoint to full contraction at the top, then finish with 7 full-range reps. This sequence maximizes time under tension across the entire strength curve of the bicep curl.

Can 21s be done with dumbbells or a cable instead of a barbell?

Yes. Dumbbells allow for a supinated grip through the full range and can reduce wrist discomfort. A cable machine provides constant tension, which is especially beneficial in the bottom stretched position where a barbell provides very little resistance. The protocol of 7 plus 7 plus 7 applies to all variations.

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