External video — Bicep Curl 21s by Theory of Motion Exercise Library.
How to do it
- Setup
- Standard barbell curl grip, hands shoulder-width, standing tall, elbows pinned to your sides.
- Execution
- Three phases, back to back, no rest between them, 21 reps total in one set. Phase 1 — 7 reps in the bottom half: from arms fully extended up to elbows bent roughly 90° (forearms parallel to the floor). Phase 2 — 7 reps in the top half: from that 90° point up to full elbow flexion. Phase 3 — 7 reps of the full range, extended to fully flexed, every rep.
- Common error
- Swinging the torso or leaning back once the biceps fatigue — this happens most in phase 3, which is exactly where strictness matters most, not least. If you need momentum to finish a rep, the set is over.
- Feel
- A burn that builds through phase 1, spikes in phase 2, and peaks hard in phase 3 — it should hurt more than a normal set of curls. If phase 1 felt harder than phase 3, you lost strict elbow position somewhere in the set.
7 reps bottom half, 7 reps top half, 7 reps full range — no rest between the three phases.