- Grasp a barbell of desired weight in with both hands (keeping in mind that 21 consecutive repetitions are performed when doing this exercise) and, either sit on a bench or stand upright (with legs about shoulder-width apart), letting your arms hang at your sides. Note: Generally this exercise is done with the forearms supinated (thumbs pointing outward). See "Further Clarification" for more details.
- Bottom Portion. Begin by curling the weight upward until your forearms are parallel with the ground, i.e. stop when you reach halfway up (midpoint), while exhaling throughout the movement.
- Lower the weight to the initial position, while inhaling throughout the movement.
- Repeat steps 2-3 until a total of 7 repetitions are reached.
- Top Portion. Without resting, curl the weight completely to top as you would in a traditional biceps curl, while exhaling throughout the movement.
- Lower the weight until your forearms are parallel to the ground, i.e. stop when you reach halfway down (midpoint), while inhaling throughout the movement. (Notice that since your first curl was a complete curl, when you now lower the weight only halfway you are working only the top portion of a traditional biceps curl.)
- Repeat steps 5-6 until a total of 7 repetitions is reached, lowering the weight all the way down on the last (7th) repetition.
- Full-Range Curls. Once again without resting, curl the weight the entire range, exhaling throughout the movement.
- Lower the weight to the bottom, inhaling throughout the movement.
- Repeat steps 8-9 until a total of 7 repetitions are reached.
Performing this exercise in front of a mirror may aid in assuring that proper form is achieved, as working within the pre-designated ranges is preferred. This exercise is bestowed its nickname, 21s, because its 3 sets of 7 repetitions equals 21 total repetitions.
By merely changing the way your forearm (and, consequently, hand) is positioned you can adjust which/(how the) muscles will be targeted, to at least some degree; this is done through pronation and supination of the forearm. Performing 3-part curls / 21s with a supinated grip (underhand with thumbs pointing away from the body), the biceps brachii bear the brunt of the exercise. Utilizing a pronated grip (overhand grip with thumbs pointing toward the body), the brachioradialis of the forearm is targeted.
Some people may develop elbow (tendon) pain if they do curls incorrectly. Three things to remember to greatly reduce the chance of elbow injury are:
- Always control the weight, especially during the down movement. Letting the weight drop as the elbow reaches the bottom "locked" position causes tremendous stress on it that will eventually likely result in injury.
- Keep your wrists straight (neutral). It is in this manner that maximum biceps stress will be achieved. Bending your wrist in either direction (upward or downward) removes focus from the intended muscle, the biceps, and creates vulnerability to injury (elbow or wrist).
- Keep your elbows at your side throughout the movement, especially if you are a novice. Many people can raise their elbows (forward) at the top of the curl movement without becoming injured, though by raising the elbows the anterior deltoids become far more involved. If you are looking for a shoulder workout, then shoulder exercises better serve this purpose. However, there are experts who claim that raising the elbows forward allows for a fuller contraction of the biceps. Use good judgment when determining whether or not to perform curls this way.