I recently wrote an article on the best cluster variations which includes everything you need to know about them. Here's a recap:

1. A cluster is a series of singles (one-rep efforts) done with a short rest interval in between. For example, a cluster set could be a series of 5 singles with 20 seconds of rest in between them. You would then rest three to four minutes before doing the next set.
2. It focuses on heavy weight. Normally ranging from 87.5 percent up to 97.5 percent of 1RM depending on the type of cluster you're doing.
3. It works by improving the fast twitch fibers' firing rate. And also by inhibiting the Golgi tendon organs, improving intramuscular coordination, and getting you more comfortable with heavy lifting.
4. There are a few cluster variations you could use. There's the Poliquin cluster (5 reps in a set with 15-20 seconds of rest), the Miller extensive cluster (5-6 reps with 30-45 seconds of rest), the Miller intensive cluster (2-4 reps with 45-60 seconds of rest) and the Mentzer cluster (5-6 reps, 3 with around 95% and 2-3 with around 85%, with 30-45 seconds of rest).

Strength

Clusters are extremely effective at increasing strength. The higher rep variations (Poliquin, Milller extensive and Mentzer clusters) are also effective for building muscle mass, especially in advanced lifters.

This program should allow you to significantly increase your strength over 12 weeks. I've seen progress as high as a 40 kilogram gain on squats in an advanced athlete (world class track cyclist), going from 180 kg up to 220 kg. His bench also went from 100 kg to 140 kg.

Editor's note: One kilogram is 2.2 pounds.

Not everybody will gain as much strength, of course. But an increase of 10-20 percent on the big lifts is pretty huge.

Muscle Growth

While it's not a bodybuilding program, it will still allow you to build mass in the process of getting strong. A pro football player I work with gained six pounds of muscle in a couple months on a cluster program. That might not seem huge, but that was without any increase in fat, and it was on the frame of someone who's been lifting hard for a decade.

If you're lean enough, it'll also make you look hard. This type of training increases myogenic tone (tonus) more than any other approach. Myogenic tone is nothing more than a partial state of muscle activation. And the more efficient your nervous system is, the higher your muscle tone becomes. Clustering is the best method for improving neurological efficiency.

Another benefit? It gets you really comfortable and efficient at handling near-maximal and maximal weights. This will not only help make you stronger on 1RM lifts, but it'll decrease the stress response that comes from future heavy lifting sessions, allowing you to do them more often or recover faster.

There are five main variables that can increase cortisol and the resulting adrenaline output during a workout. And while both (cortisol and adrenaline) are necessary to perform optimally, too much can lead to a decrease in performance and gains.

We easily understand how excessive cortisol can lead to decreased muscle growth: it increases muscle breakdown, reduces protein and glucose uptake by the muscles, can increase myostatin, and – in the long term – lead to lowered testosterone levels.

But why is too much adrenaline a bad thing? Well, if you produce too much it will linger in your body for a longer time, staying attached to the beta-adrenergic receptors. These receptors are prone to downregulation/desensitization.

A study by Fry and colleagues showed that two weeks of very intense lifting (maxing out five days a week) can decrease receptor sensitivity by close to 40 percent.

When that happens, your body has a much lower response to your own adrenaline. This leads to lowered force and power production, less focus and motivation, lower energy levels, etc. It'll also lead to higher cortisol levels for the same stress levels: the body has to produce more cortisol to get the job done.

Why is that important and relevant to this program? Let's look at the five main training variables that can have an impact on cortisol and adrenaline production:

1 Volume

One of the main functions of cortisol is energy mobilization. The more energy you need, the more cortisol you produce. A higher volume approach will therefore lead to a higher cortisol level.

2 Intensiveness

This is how hard you're pushing your sets. The closer you go to failure, the more the body perceives that set as an intense stress. The response is to increase cortisol, which will increase adrenaline. This boosts your strength, mental awareness, and motivation to survive.

3 Psychological Stress

If a weight (or task) is intimidating and even scares you a little, the body will release more cortisol, which increases adrenaline so that you'll have the physical and mental resource to fend off any potential danger. In weight training, this is often associated with maximal or near-maximal weights, especially on exercises where the spine is under load.

4 Neurological Demands

This refers to how hard your nervous system must work during the session. Some training-related factors that will increase neurological demands are: using more complex exercises, using exercises you haven't mastered yet, having lots of exercises in a workout, going heavy, doing explosive work, alternating two exercises (A1/A2), doing circuits, using several completely different methods and intensity zones in a workout.

5 Density

The higher your work-to-rest ratio is, the more adrenaline will stay elevated. This means both higher cortisol and adrenaline production.

In the cluster program, the intensiveness is high, the psychological stress is very high, and the neurological demands are fairly high because of the exercise selection (big compound movements) and the heavy loads used.

The last thing you want is to increase neurological demands even more by adding a lot of assistance work. So you'll now have three cortisol/adrenaline producing factors very high. Not sustainable for more than three weeks for most.

It's also why the overall volume needs to stay low, which is another reason to avoid adding a lot of assistance work. Because of the minimal nature of the program, the density is low, so that's not an issue.

There are four workouts per week. Each workout focuses on a big lift: a squat variation, a horizontal press variation, a deadlift/hip hinge variation, and an overhead/incline press variation.

One multi-joint assistance exercise is added after the main lift and one or two minor movements are done after that. Both the main and the primary assistance exercises use a cluster approach, for two or three work sets.

The minor exercises are done using an intensification technique like rest/pause or mechanical drop sets for one to two work sets to failure.

As you can see, the volume is fairly low: seven to nine work sets per workout, allowing you a higher intensity and intensiveness.

Because there will be 20-60 seconds of rest between reps in the main exercises, and up to four minutes between sets, the density is very low too. This, and the lower volume, are super important to be able to tolerate the high intensity for the duration of the program.

The program is segmented into three-week blocks and there are four of them total. Each block uses a different cluster approach, gradually increasing in intensity.

Each workout will include three to four exercises. The first two multi-joint exercises of each session are done as clusters. The primary movement is your main lift of the day, the one you want to increase the most. It stays the same for the duration of the program.

The main assistance lift is a movement aimed at strengthening the primary lift. It can be a variation of the primary lift, a partial movement, or a different exercise hitting key muscles in the primary lift. The main assistance movement can change every block.

The last two exercises are less demanding neurologically. They'll be either isolation lifts or multi-joint lifts done on machines or pulleys. These are not done as a cluster. You'll use either a drop set, myo-reps, or rest/pause, depending on the block.

Now let's look at the template for exercise selection, so that you can easily design the program yourself.

You can use whatever primary exercises you want, as long as you respect the logic of the program. Pick from:

Day 1 – Squat Variation

• Back squat
• Front squat
• Low-bar squat
• Safety bar squat
• Box squat
• Zercher squat

Day 2 – Horizontal Press Variation

• Bench press
• Decline bench press
• Floor press
• Football-bar bench press
• Duffalo/buffalo bar bench press

Day 3 – Deadlift/Hip Hinge Variation

• Conventional deadlift
• Sumo deadlift
• Trap-bar deadlift
• Power clean variations
• Power snatch variations

Day 4 – Vertical/Incline Press Variation

• Military press
• Push press
• Incline bench press (30 degrees)
• High-incline bench press (60 degrees)

Now select the exercises you'll do after the main lifts:

Day 1 – Squat

Block 1

• Heels-elevated front squat
• Heels-elevated back squat
• Narrow-stance squat
• Hack squat machine

Block 2

Different squat variation than primary lift from the same list. For example, if your primary lift is the back squat you can do front squat, Zercher squat, or box squat.

Block 3

Choose an overload squat exercise:

• High-box squat
• Squat or front squat from pins knees starting at 90 degrees
• Squat or front squat with chains (80% on the bar and a top weight of 100-110%)
• Squat or front squat with weight releasers lowered slowly (75-80% bar weight and an extra 25-30% on the releasers)

Block 4

No main assistance lift (to allow more work on the primary)

Day 2 – Bench Press

Block 1

• Close-grip bench press
• Close-grip decline bench press
• Close-grip floor press
• Close-grip football bar bench press

Block 2

Different bench press variation than primary lift from the same list.

Block 3

Choose an overload bench exercise:

• Bench press from pins from mid-range
• 3-4 board press
• Half-range bench press
• Bench press with chains
• Bench press with weight releasers lowered slowly

Block 4

No main assistance lift.

Day 3 – Deadlift/Hip Hinge

Block 1

• Deficit deadlift
• Deficit sumo deadlift
• Snatch-grip deadlift
• Deadlift with heels elevated
• Double overhand no-straps deadlift
• Good morning
• Zercher good morning

Block 2

Different deadlift/hip hinge variation than primary lift from the same list.

Block 3

Choose an overload hip hinge movement:

• Pin pull from below the knees
• Deadlift with chains (80% on the bar and a top weight of 100-110%)
• Sumo pin pull from below the knees

Block 4

No main assistance lift.

Day 4 – Vertical/Incline Press

Block 1

• Very high incline press (75 degrees)
• Close-grip incline press (30 degrees)
• Close-grip high incline press (60 degrees)
• Behind the neck press

Block 2

Different vertical/incline press variation than primary lift from the same list.

Block 3

Choose an overload vertical/incline press movement:

• Push press (if it wasn't your primary)
• Military press from pins starting at forehead
• Incline bench press (30 degrees) from pins starting at mid-range
• High incline bench press from pins starting at mid-range (60 degrees)

Block 4

No main assistance lift.

The role of these exercises is mostly to hit what's neglected by the two main lifts. For instance, the back and hamstrings would be the most important to work on. You could use two upper back exercises on each upper-body session and two hamstring exercises for the lower-body sessions. That's what I recommend.

What about arms? This program is aimed at maximizing strength while also giving you an overall thicker, denser, and bigger physique. You can spend more time on your arms after the program is done. But during this program, you'll be doing a lot of heavy pressing work. I guarantee your triceps will grow even without direct stimulation.

Day 1 – Squat

Pick one exercise from each category in the list for each workout. You can also use your own preferred movements.

Posterior Chain:

• Glute-ham raise
• Reverse hyper
• Rope pull-through
• Lying leg curl
• Standing leg curl
• Inverted leg curl
• Nordic hamstring curl
• Back extension
• Hip thrust

Quads:

• Hack squat
• Leg press
• Leg extension
• Sled backward walk (1 rep is 10 meters)

Day 2 – Bench Press

Rhomboids/Rear Delts:

• Seated row (various grips)
• T-bar row
• Landmine row
• Chest-supported row
• Seal row
• Face-pull
• Rear delt raise
• Reverse pec deck
• Band pull-apart

Lats:

• Pull-up (various grips)
• Lat pulldown (various grips)
• Pullover
• Straight-arm pulldown
• Pullover machine

Day 3 – Deadlift/Hip Hinge

Posterior Chain:

• Glute-ham raise
• Reverse hyper
• Rope pull-through
• Lying leg curl
• Standing leg curl
• Inverted leg curl
• Nordic hamstring curl
• Back extension
• Hip thrust

Traps:

• Barbell shrug
• Dumbbell shrug
• Zercher shrug
• Rope upright row
• Kirk shrug
• Single-arm barbell shrug
• Band pull-apart to forehead level

Day 4 – Overhead/Incline Press

Rhomboids/Rear Delts:

• Seated row (various grips)
• T-bar row
• Landmine row
• Chest-supported row
• Seal row, face-pull
• Rear delt raise
• Reverse pec deck

Lats:

• Pull-up (various grips)
• Lat pulldown (various grips)
• Pullover
• Straight-arm pulldown
• Pullover machine

The program has four blocks lasting three weeks each. The methods/loading scheme changes at every block.

Block 1 – First 3 Weeks

A. Main Lift – Modified Poliquin Clusters

• Sets: 3 work sets (2-3 gradually heavier preparation sets of 3-5 reps, not as clusters)
• Reps: 5-6 cluster reps
• Rest between reps: 20 seconds
• Load: 87.5% (starting point)
• Rest between sets: 4 minutes

B. Primary Assistance Exercise – Modified Poliquin Clusters

• Sets: 2 work sets (2-3 gradually heavier warm-up sets of 3-5 reps, not as clusters)
• Reps: 5-6 cluster reps
• Rest between reps: 20 seconds
• Load: 87.5% (starting point)
• Rest between sets: 4 minutes

C & D. Secondary Assistance Exercises – Drop Set

• Sets: 1-2 work sets (1-2 warm-ups, not as drop sets)
• Reps: 8-10, then drop by 20% and get as many quality reps as possible
• Load: Around 70% then 50%
• Rest between sets: 3 minutes

Block 2 – Second 3 Weeks

A. Main Lift – Miller Extended Clusters

• Sets: 3 work sets after preparation sets
• Reps: 5-7 cluster reps
• Rest between reps: 30-45 seconds (30 on the first set, 40 on the second, 45 on the third)
• Load: 90% (starting point)
• Rest between sets: 4 minutes

B. Primary Assistance Exercise – Miller Extended Clusters

• Sets: 2 work sets after preparation sets
• Reps: 5-7 cluster reps
• Rest between reps: 35-45 seconds (35 on the first set, 45 on the second)
• Load: 90% (starting point)
• Rest between sets: 4 minutes

C & D. Secondary Assistance Exercises – Modified Myo Reps

• Sets: 1-2 work sets (1-2 warm-ups, not as myo rep sets)
• Reps: 6-8 initial reps, then perform as many micro-sets of 3 reps as possible with 5 deep breaths in between
• Load: Around 70-75%
• Rest between sets: 3 minutes

Block 3 – Third 3 Weeks

A. Main Lift – Modified Mentzer Clusters

• Sets: 3 work sets after heavier preparation sets
• Reps: 5-6 cluster reps
• Rest between reps: 30-45 seconds (30 on the first set, 40 on the second, 45 on the third)
• Load: 95% for the first three reps, then drop down to 85% for 2-3 more reps
• Rest between sets: 4 minutes

B. Primary Assistance Exercise – Modified Mentzer Clusters

• Sets: 2 work sets (after gradually heavier preparation sets of 3-5 reps, not as clusters)
• Reps: 5-6 cluster reps
• Rest between reps: 30-45 seconds (35 on the first set, 45 on the second)
• Load: 92.5-95% for the first three reps, then drop down to 85% for 2-3 more reps
• Rest between sets: 4 minutes

C & D. Secondary Assistance Exercises – Heavy Rest/Pause

• Sets: 1-2 work sets (1-2 warm-ups, not as myo reps sets)
• Reps: 4-6 initial reps, rest 15 seconds and get as many extra reps as possible with the same weight
• Load: Around 85%
• Rest between sets: 3 minutes

Block 4 – Final 3 Weeks

A. Main Lift – Miller Intensive Clusters

• Sets: 4-5 work sets (after gradually heavier preparation sets of 3 reps, not as clusters)
• Reps: 2-4 cluster reps
• Rest between reps: 45-60 seconds (45 on the first set, 50 on the second, 60 on the third)
• Load: 95-97.5% (starting point)
• Rest between sets: 4 minutes

B. Primary Assistance Exercise – None

C & D. Secondary Assistance Exercises – Normal reps (to allow the greater workload on the main lift)

• Sets: 2-3 work sets (1-2 warm-ups)
• Reps: 8-10 reps (1-2 reps left in the tank)
• Load: Around 70-75%
• Rest between sets: 3 minutes

The percentages are just to give you an idea of a starting point.

In reality you want to use a load that represents an effort of around 9/10, where maybe you could've gotten one more cluster rep.

Select the weight based on your performance.

It's perfectly fine to start conservatively on the first set and add weight if you can reach the top of the zone. It's also fine to go down in weight if you overestimated your capabilities.

Progress the same way.

For example, if you finished week 1 with 300 pounds for 5 reps on your heaviest cluster and it was a 9/10, maybe you can start your first set of the next week there. Then adjust the weight for your other sets based on how that set went. I'd like to give you a precise mathematical formula to select the weekly weight, but clusters are different than normal sets. Predicting progress is almost impossible to do.

Can you add conditioning work?

It's possible to do it, in small amounts. Ideally, the conditioning work would be done separately, either as a second workout in the day or on one of the days off. You can also add 10-15 minutes of low intensity cardio pre and post-workout without problems.

Can you add abdominal work?

Yes, no problem. It causes very little systemic and neurological fatigue. I'd add it at the end of the lower-body sessions.

Can you add forearm and calf exercises?

These also can be added. However, I don't want you to shotgun additional work. Adding ab work is fine, adding one bicep exercise is fine, adding forearm work is fine. But adding two of them in a session isn't recommended.

Can you do this while dieting down?

It's possible. The volume is low and most of the stress is neurological, so you should be able to recover. No program will yield maximum gains when you're in a caloric deficit though.