21s Bicep Curls
Targets the biceps
Requires a cable machine
Intermediate level
Maximises time under tension for muscle growth
A classic technique used by bodybuilders
Step 1
Attach a short bar to the cable pulley set at the lowest position. Stand facing the machine, half a step back, with feet shoulder-width apart. Grip the bar with an underhand grip (palms facing up) and let your arms hang straight in front of you. Stand tall with your core braced and elbows tucked close to your sides. This is your starting position.
Step 2
Bottom halves (7 reps): curl the bar from the starting position up to belly-button height, keeping your elbows fixed at your sides. Lower back to the start. Repeat this bottom-half movement 7 times in total.
Step 3
Top halves (7 reps): from belly-button height, curl the bar all the way up to your chest. Lower back to belly-button height. Repeat this top-half movement 7 times in total.
Step 4
Full reps (7 reps): curl the bar from the fully extended starting position all the way up to your chest, then lower with control back to the start. Repeat for 7 full reps. That's one complete set of 21s — 7 bottom halves, 7 top halves and 7 full reps.
Exercise Benefits
21s bicep curls are a classic bodybuilding technique that divides a full curl into three zones, keeping the bicep under tension for the entire set. The bottom half emphasises the stretched position, the top half emphasises the contracted position, and the full reps hit both. That extended time under tension is one of the most effective ways to stimulate muscle growth, making this a great exercise to add when your standard curls start to feel stale.
