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21s

A curl variation combining partial and full reps in a structured sequence, building both strength and endurance in one set.

Setup

Grip the bar with arms extended, standing tall. Same starting position as a standard curl.

Movement

Perform 7 reps through the bottom half of the range. From full extension to roughly halfway up, then back down. Perform 7 reps through the top half of the range. From halfway up to full contraction, then back to halfway.

Return

Perform 7 full-range reps. Complete the set with standard, full-range curls.

Common Mistake to Avoid

Using the same weight as a full-range set. Because of the significant time under tension, this technique typically requires lighter weight than standard curls.

Equipment Barbell or EZ-bar
Primary Muscles Biceps
Secondary Muscles Forearms

Why it matters

This technique breaks a curl into three distinct 7-rep phases — bottom-half partials, top-half partials, then full reps — within a single set, creating significant time under tension and a different kind of fatigue than standard full-range sets. It's a popular intensity technique for adding variety and volume to bicep training.

How to do it

  1. Grip the bar with arms extended, standing tall. Same starting position as a standard curl.
  2. Perform 7 reps through the bottom half of the range. From full extension to roughly halfway up, then back down.
  3. Perform 7 reps through the top half of the range. From halfway up to full contraction, then back to halfway.
  4. Perform 7 full-range reps. Complete the set with standard, full-range curls.

Common mistakes

  • Using the same weight as a full-range set. Because of the significant time under tension, this technique typically requires lighter weight than standard curls.
  • Rushing through the partial-rep phases. Each phase should be performed with the same control as a full rep, just through a limited range.
  • Losing strict elbow position across all 21 reps. Fatigue tends to build throughout the set — maintain the same elbow-pinned form even as it gets harder.
  • Skipping a phase or rushing the total count. All three phases, performed deliberately, are what make this technique effective.

Sets & reps by level

Beginner

Not typically recommended for true beginners — master standard curls first.

Intermediate

2–3 sets of the full 21-rep sequence with light to moderate weight.

Advanced

3 sets of the full 21-rep sequence, often used as a finishing technique at the end of an arm workout.

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