The real "magic" in any training program is in the methodology. Only newbies talk about exercises. Advanced lifters, on the other hand, talk about methods. One such method is the cluster set. When I need more strength and size, I always go back to clusters. And now I have a new way to make them even more effective.

Classic Cluster Sets

Cluster sets are one of the most powerful, growth-inducing methods for intermediate and advanced lifters. A typical set looks like this:

  1. Load the barbell to 90% of your maximum, a weight you could normally lift 3 times.
  2. Do one rep and rack the bar.
  3. Rest 10 seconds.
  4. Do another rep and rack the bar.
  5. Rest for 10 seconds.
  6. Continue in this manner until you reach the maximum number of reps you can do, which should be between 4 and 6 reps.

So clusters refer to doing a set of several reps, but taking a short rest between each rep. You're using 85% to 95% of your maximum, which is usually your 5RM. The total reps per set are kept low to moderate (4 to 6), and the rest between repetitions is about 10 seconds.

Why Are Clusters So Effective?

Clusters allow you to perform more work than you'd normally be capable of at a given weight. The short rest periods between reps allow you just enough time to replenish some ATP in the muscles so you can continue at a high level of intensity.

The key to making muscle grow and getting as strong as possible is recruiting high-threshold motor units – fast-twitch fibers. These motor units earned their name because they're only involved when a very intense muscular effort is needed. The most important factor in stimulating fast-twitch fibers is the intensity of the load relative to your maximum. So the closer a load is to your max, the more high-threshold motor units pitch in to help lift the weight.

But it's not enough to just recruit a muscle fiber to get it to grow. To quote Zatsiorsky from Science and Practice of Strength Training,

"A muscle fiber that is recruited but not fatigued is not trained."

Fatigue Muscle Fibers for Growth

In other words, don't just recruit muscle fibers, fatigue them – which requires ample repeated efforts of the the same exercise. This is why doing heavy sets of only 1 or 2 reps doesn't work well in making you bigger. Sure, you recruit a lot of muscle fibers, but you don't fatigue them.

Clusters take care of that problem. You use heavy loads to help you recruit a maximum amount of muscle fibers. You also utilize short rest intervals between reps that allow you to replenish ATP and do more total reps per set. Even though you're resting about 10 seconds between reps, it's not enough to allow the fibers to recover. Consequently, you're not only recruiting fibers, you're fatiguing them as well, which means muscle growth. That's great, but it could be better.

A Better Method – Maximum Growth Clusters

The classic cluster has a been a key part of my arsenal for over 15 years. Lately, I decided to push cluster development further and experiment to make it even better. The key was to bring in all three mechanisms of hypertrophy.

The 3 three pathways that stimulate muscle growth:

  1. Muscle damage and mechanical stress
  2. The release of local growth factors
  3. The activation of the mTOR pathway

Regular clusters shine when it comes to muscle damage and mechanical stress, but they neglect the other two hypertrophy pathways: the release of local growth factors and the mTOR pathway. So if we want to make clusters even more effective, we should find a way to include these two elements.

What are growth factors?

Growth factors are released in working muscle from an accumulation of metabolites (lactate, hydrogen ions) and hypoxia – lack of oxygen in muscle due to constant tension. Neither of which is maximized during a set of regular clusters. What does increase the release of growth factors is having the muscle in an uninterrupted state of constant tension for a long enough time for the muscles to "burn." Traditionally, the best way to do this is to use lighter weights and do reps relatively slowly, squeezing the muscles hard during every inch of every rep.

Negatives Play a Role

Stimulating hypertrophy through the mTOR pathway is activated whenever you lift weights, but there's one type of contraction that really turns it on: accentuating the eccentric (lowering) portion of the lift. That means lowering the weight fairly slowly, especially when using heavy weights. This will drastically increase mTOR activation and therefore muscle growth.

Two Ways to Maximize Clusters

Let's start with our classic cluster and add to it to activate mTOR even more and increase the release of growth factors.

  1. Activate the mTOR Pathway. Perform your cluster reps with a fairly slow eccentric or negative portion. Lowering the weight in 4 seconds while tensing the muscle will be more than enough to reap all the benefits. Yes, that means you might use slightly lighter weights, but if you stay at 85% or more it'll be enough to recruit the maximum number of muscle fibers. Just don't drop down too much – lower than 80% of 1RM – or you'll lose the benefits.
  2. Stimulate the Release of Growth Factors. The second missing element, constant tension, can't be added to the cluster itself. But what you can do is add a "drop set." Immediately after your 4-6 cluster reps, decrease the weight then continue your set with constant tension reps to failure (about 8-10 reps.)

A Max-Growth Cluster Set

Starting Weight: 225 pounds
All reps done with a 4 second lowering phase.

  • 1 rep rest 10 seconds
  • 1 rep rest 10 seconds
  • 1 rep rest 10 seconds
  • 1 rep rest 10 seconds
  • 1 rep no rest

Immediately drop to 150 pounds. Do 8-10 reps with constant tension – controlled repetition tempo, no lockout at the top.

What Weight to Use – To be optimally effective, the load should be 85% or more.

At first you might have to use a bit less weight to get used to the intensity, but under no circumstance should you use less than 80%. Work up to being able to handle 85-90% for all work sets.

How Long to Rest – You'll need plenty of rest between sets.

Max-Growth Clusters end with constant tension reps which will lead to an intense accumulation of metabolites in the muscle and hinder force production until properly recovered. Your first priority with Max-Growth Clusters is to handle heavy weights, not get a pump. The constant tension reps are an add-on to make the set more effective, but the add-on shouldn't detract from the main workload. Using longer rest intervals in this instance is mandatory. You might lose some performance between sets, but you should stick to the same starting weight. If necessary, drop one cluster rep (maybe go from 6 to 5, or 5 to 4). That's fine as long as you stay in the 4-6 range with the correct load.

How Many Sets to Do – Unlike classic cluster sets, which require about 5 sets, you only need 3 with Max-Growth Clusters.

Exercises – This method can work with any exercise. People might assume it only works with big, compound movements, but it works with anything, even machine curls.

Related:  More on increasing mTOR

Related:  The Magic of Cluster Sets