Everyone knows 21s, the classic biceps movement ripped straight from the pages of Arnold's Encyclopedia of Modern Bodybuilding.

If not, here's the quick 'n dirty:

  1. Perform 7 reps of top-range partial biceps curls where you only lower the bar halfway.
  2. Then do 7 reps of low-range partial biceps curls stopping halfway up.
  3. Finish with 7 full range of motion (ROM) reps for a total of 21 painful reps.

Despite their old-school underpinnings, 21s are still a very effective training protocol, and one that needn't be reserved for just biceps.

Twenty-ones and its new variations are simply overload techniques that work by increasing the time under tension (TUT). Increasing the TUT increases metabolic stress, one of the three mechanisms for increasing muscle hypertrophy described in Brad Schoenfeld's seminal research paper (1).

These techniques also give you an incredible pump, which is also related to hypertrophy through "cell swelling."

The biggest difference between these new versions of 21s and the traditional method is that these protocols focus more on the mid-range of the exercise. The reason for this has to do with a principle of physiology known as the length-tension relationship or thelength-tension curve. Put simply, this is the relationship between the length of the muscle fiber and the force the fiber produces at that length.

Muscles have the lowest potential to generate force when they're either fully elongated (stretched) or fully shortened (contracted). They generate the highest possible tension in the middle – halfway through the range of motion.

Another reason to focus on the mid-range is because it's the position where maximal loading of the biceps occurs. During any curl, the biceps are maximally loaded (stimulated) at the point in the ROM where the forearm is at a 90-degree angle with the load vector. If you're using free weights, gravity is the load vector, so the point of maximal loading is where the elbow reaches 90 degrees of flexion or when your forearm is parallel to the floor.

The farther away you move from a 90-degree angle with the load vector, the shorter the lever arm becomes and the less work your biceps have to do. That's why in a free-weight biceps curl, the closer you move toward the bottom or top of the range, the less work your biceps get because the lever arm is shortening. It's also why lifters doing barbell or dumbbell curls typically rest between reps at the top and bottom position.

Now that the rationale behind focusing more on the midrange is clear, let's look at some practical applications.

Version A

Perform this protocol using dumbbells, a barbell, or with an EZ-Curl bar.

  • 7 x Mid-Range Partial Reps
  • 7-Second Isometric Mid-range Hold w/ Wrist Pronation-Supination
  • 7 x Full Range of Motion Reps

Version B

Perform this protocol using two sets of dumbbells. Begin with the lighter set and perform the first exercise, then switch to a pair that's 5 pounds heavier and perform the other two exercises. For example, start with 20-pound dumbbells, then switch to 25-pound dumbbells.

  • 7 x Leaning Biceps Curls
    (switch to heavier dumbbells)
  • 7-Second Isometric Mid-Range Hold w/ Wrist Pronation-Supination
  • 7 x Full Range of Motion Reps

Note: You can also use leaning curls as a stand-alone biceps exercise.

I've never understood why bodybuilders apply 21s only to their biceps. The way I see it, 21s are a simple and versatile overload technique that can easily be applied to almost any strength exercise.

That said, as with all other overload methods, certain techniques work better with some movements more than others.

Dumbbell Shoulder Press 21s

This protocol is performed with dumbbells. You can perform it either seated or standing. Since the lever arm is the longest in this exercise when the humerus is parallel to the floor, the isometric is performed in that position.

  • 7 x Mid-Range Partial Reps
  • 7-Second Mid-Range Isometric Hold, opening and closing your arms (Arnold press style)
  • 7 x Full Range of Motion Reps

Dumbbell Chest Press 21s

This one can be done using dumbbells or with a barbell. Since the lever arm is the longest in this exercise when the humerus is parallel to the floor, the isometric is performed in that position.

  • 7-Second Isometric Mid-range Hold
  • 7 x Full Range of Motion Reps
  • 7 x Partial Reps (at the top range)

Lat Pull Down 21s

You can do this protocol using a neutral, wide, or underhand grip. I like to use a different grip each time to create a different stimulus. The isometric is performed at the bottom position as this is the point of the ROM where most people cheat.

  • 7 x Mid-Range Partial Reps
  • 7-Second Isometric Hold, bottom-range (full contraction)
  • 7 x Full Range of Motion Reps

Bent Over Row 21s

You can do this protocol using dumbbells, a barbell, or on a seated row machine. The isometric is held at the full contraction because it forces you to focus at the top of the row, the part of the exercise where most people cheat.

Also, if you're using free weights you can vary your torso lean from a 45-degree angle to parallel to the floor, thereby hitting your muscles a bit differently.

  • 7 x Top-Range Partial Reps
  • 7-Second Isometric Hold, top-range (full contraction)
  • 7 x Full Range of Motion Reps

If you're looking to add even more work-volume, you can go up a notch and try the 28s protocols.

To perform 28s, all you do is add 7 partial ROM reps – either top range partials or bottom range partials – to the beginning or end of any of the 21s protocols shown above. It's up to you what type of partial reps you feel best fits with the protocol, along with where in the protocol you'd like it to go (in the beginning or at the end).

Also, keep in mind that you don't have to only use 7 reps, as "7" certainly isn't a magic number. Maybe you'd prefer to do 6 reps of each exercise? Or maybe you hit these protocols with a countdown style, where you do the first exercise for 8 reps, the second for 7 reps/seconds, and the third for 6 reps.

Regardless of how you spin it, these protocols will increase work volume, TUT, and therefore metabolic stress.

How Many Sets?

Perform 21s and 28s protocols for 1-2 sets, with 90 seconds to 3 minutes of rest between sets. Since these protocols involve lighter loads performed at high volumes, they're best performed at the end of a comprehensive strength-training workout.

  1. Schoenfeld BJ. The mechanisms of muscle hypertrophy and their application to resistance training. J Strength Cond Res. 2010 Oct;24(10):2857-72. PubMed.
  2. Grant AG et al. Regulation of protein synthesis in lactating rat mammary tissue by cell volume. Biochim Biophys Acta. 2000 Jun 1;1475(1):39-46. PubMed.
  3. Stoll B et al. Liver cell volume and protein synthesis. Biochem J. 1992 Oct 1;287 ( Pt 1)(Pt 1):217-22. PMC.
  4. Millar ID et al. Mammary protein synthesis is acutely regulated by the cellular hydration state. Biochem Biophys Res Commun. 1997 Jan 13;230(2):351-5. PubMed.
  5. Lieber RL et al. Skeletal muscle mechanics: Implications for rehabilitation. Phys Ther. 1993 Dec;73(12):844-56. PubMed.
  6. Smith LK et al. Brunnstrom's Clinical Kinesiology (5th ed.) Philadelphia. F.A. Davis. 1996.
  7. Winter D. Biomechanics and Motor Control of Human Movement. New York. John Wiley. 1990.