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Hypertrophy training – Matrix 21s

Hadyn Luke posted this on Tuesday 10th of April 2018 Hadyn Luke 10/04/2018

Tags: Training methods

21's matrix large

As with other hypertrophy training methods – discussed in our blogs on Hypertrophy Training, Escalating Density Training, German Volume Training, Peripheral Heart Action Training and Drop Sets – Matrix 21s are designed to increase muscle size.

Considered “old school” by many personal trainers and bodybuilders, Matrix 21s are nonetheless an effective training method, with variations introduced over the years to bring them up to date with newer training techniques.

What are Matrix 21s?

Also known as 21s or partials, Matrix 21s comprise a single set of exercises targeting a particular muscle or muscle group using three phases of motion – an outer, inner and full range.

The 21 in the name refers to the number of reps, which are split into 3 x 7 reps for the three ranges of motion (ROM).

The process is as follows:

  • 7 reps in the outer half of your range of movement
  • 7 reps in the inner half of your range of movement
  • 7 reps in your full range of movement

The 21 reps are carried out one after another and then followed by a rest of 60 to 90 seconds.

Most gym goers will be familiar with using Matrix 21s for bicep curls but fitness professionals will be able to advise on a range of other exercises that can be carried out using this formula.

How do Matrix 21s work?

This exercise format works by training muscles in a different way from usual, with concentric (shortening muscle exercises), eccentric (when a muscle lengthens) and full-range reps all combined in one exercise (see our blog on: Contraction types and how a personal trainer can use them).

Increasing the amount of time under tension, particularly in the final full-range seven reps, helps to shock the system, work the muscle and build muscle mass.

What variations can be applied to this exercise?

One option is to play around with the number of reps, another is to vary the range of motion involved.

In recent years, it has been suggested that you should carry out more reps in the middle section of the set. This is related to the length-tension relationship or curve. Eccentric training, where the muscle lengthens, is believed to increase the isometric force exerted by the muscle, bringing more effective results.

What sort of exercises can Matrix 21s be applied to?

As the basis of Matrix 21s is to overload the muscle, there is no reason they can’t be applied to a range of exercises beyond the traditional bicep curl associated with this form of exercise.

Some of the other exercises suited to Matrix 21s training are:

  • Dumbbell shoulder press
  • Bent over row
  • Lateral raise, lateral pull down
  • Chest press
  • Cable cross-over
  • Leg extension


Matrix 21s are used by many to achieve muscle tone and gain. As the system is more about technique than heavy weights, the user is less likely to injure themselves than they might be with some other strength training methods, especially if they are training under the eye of a personal trainer or fitness instructor.

This means that Matrix 21s can be used by a wide range of gym goers of different ages and abilities, including – when properly supervised – as a tool for rehabilitation after an accident or injury.

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