A few years ago I consulted briefly with a young woman who wanted to learn Olympic Weightlifting. From our first session it was clear that she had great motivation, adequate flexibility, solid coordination but little muscle mass.
At the end of the first session she was given technical exercises to work on as well as Front Squats that were to be performed in 
the following way:
- The safety pins were placed corresponding to the height of her shoulders in the bottom position of the Front Squat.
- She was to perform one repetition at a time by stepping under the bar, setting up for and executing the squat before stepping back from the bar and repeating.
- She was instructed to do 30 repetitions one at a time – essentially 30 x 1 repetitions.
Our next session was two weeks later. Upon entering the gym, I saw the shape of what looked to be an experienced lifter with smooth technique and muscular thighs. When I got closer I saw that it was this girl who had worked diligently on the exercises I had suggested for her.
A major reason for the choice of this cluster style approach is the easily observable fact that cluster training can help athletes and clients maintain good form throughout the training of an exercise, particularly if they are relatively new to lifting.
Why? In some cases, we are able to perform the first repetition with good form but then, as fatigue sets in, the form deteriorates. With cluster training, each rep is the “first” rep.
I had known about and used Cluster Style training before, but the experience with this young girl convinced me that cluster style training has applicability both for beginners and for advanced athletes.
Cluster training is not new. The quote below is from The Rader Master Bodybuilding and Weight Gaining System, originally published in 1946 (on breathing methods during deadlift training for weight gain). (5)
Another preferred method is to stand up after each repetition (after placing the weight on the floor) and take 3-6 deep breaths between each repetition. Then grasp the weight and take a deep breath and make another repetition.
Later, renowned Olympic Weightlifting Coach, Carl Miller used Cluster Training in the 1970s. (6)
Cluster training is still used today (for example, by Dr. Stuart McGill, world renowned back specialist from Waterloo, Ontario). (7) Mc Gill uses clusters to achieve
Maximum Neuro drive during a chin-up from every part of the back and it starts with grip. Instead of sets of 6-10, consider sets of 1, 10 or so times, and working up to 15-20 singles, over time. Take about 10 seconds of rest between. 
The cluster tactic can also be used to break a larger amount of work into smaller chunks. Here is an abbreviated description of 50 rep sets from the classic Steel Tips by Dr Ken Leistner.(18)
Start weight = 20-25RM
Execution: Do as many reps as possible. Then rest 10 seconds. Repeat until all 50 Repetitions are completed.
As a strategy, cluster training is an extension of traditional training. Imagine that you were told to do 30 repetitions with 70% of your 1RM. However, you were not told that you could break the work down into 3 sets of 10 repetitions. (See Graph 1) You would stop after about 10 repetitions, frustrated that you could not complete the 30 repetitions.
Cluster Training is an example of the saying to train as much as possible, while staying as fresh as possible. (8) The real difference between traditional training and cluster training lies in the size of the chunks.
This article begins by suggesting a so-called 1st Principle of physical training. Based on the 1st Principle, strategies to achieve the Principle are discussed. Last, specific tactics for applying Cluster Training are laid out.
SECTION 1
1st Principle of Physical Training
A “principle” is a basic truth, law or assumption (thefreedictionary.com). A first principle is a basic, foundational, self-evident proposition or assumption that cannot be deduced from any other proposition or assumption. (21)
How could a 1st Principle of physical training be defined?
Athletes or fitness clients approach strength coaches and personal trainers to achieve a certain objective. Achieving this objective always requires
- A structural change in the body.
- A functional change in the body.
Thus, the 1st Principle of physical training could be defined as, to stimulate structural or functional adaptations specific to the athlete’s or fitness client’s goal.
SECTION 2
Strategies to Achieve the 1st Principle
Overall, it could be stated that the higher the intensity, volume and workload while still maintaining the ability to recover, the greater the potential for structural and functional changes.
Challenging the boundaries of adaption through the best possible balance between stress and recovery necessitates that training program is truly based on the individual abilities rather than generic standards.
Two strategies behind a broader group of research include:
- Break down the total work load into smaller chunks.
- Match the load to the capacity of the athlete-client as closely as possible, repetition by repetition throughout a set.
SECTION 3
Tactic #1: Cluster Training
The dictionary’s definition of a cluster is, a group of similar things or people positioned or occurring closely together. In the perspective of a full session, this definition also applies to a set in the traditional sense.
The research on cluster training is focused on the effects of taking rest periods within a traditional set. (9)
“Inter-repetition rest” involves rest between each repetition.
“intra-set” rest involves rest between groups of repetitions.
Rest periods between sets are referred to as inter-set rest.
Based on the terminology above, cluster training is not limited to a particular length of a set, or a particular length of a cluster. Fundamentally, all qualities of strength could be developed with cluster training.
3a. What are the Benefits of Cluster Training?
Of special interest are the results from studies that compared longer sets with longer rest between sets, with shorter sets and 
shorter rest between sets but a similar work: rest ratio. Such a re-distribution of rest periods to more frequent intra-set and inter repetition rest results in two core benefits of Cluster Training:
- More repetitions performed with a given intensity. (1,4,10,15)
- Better maintenance of peak power, force and velocity across a session (11,12,13,14,15)
It is currently less well known how these two benefits may translate into better long-term adaptations. (15)
Additional benefits of Cluster Training Include:
- Lower session RPE. (1)
- Better maintenance of exercise form across the total repetition volume.
3b. Why Does Cluster Training Work?
Force and power tend to drop from the 2nd repetition in a continuous set. (13, 14)
Partial recovery of ATP-CP stores may happen in 15-20 seconds, which may explain how force and power output can be maintained over multiple repetitions and multiple sets. (14) The (partial) recovery between repetitions allows the lifter to handle near maximal weights for many repetitions with a possible beneficial effect on hypertrophic and neural adaptations. (11, 12)
In summary, the benefits of cluster training can explained with a reduction in both central and peripheral fatigue to include the maintenance of phosphor – creatine stores and help avoid lactic build up. (1, 2, 4, 15)
Cluster training works for both dynamic and isometric contractions.
3c. Are There Any Disadvantages to Cluster Training?
- Too little fatigue.
Paradoxically, the upside of cluster training (the prevention of fatigue) is also its potential downside. Fatigue plays a role in maximal strength development through increased activation of motor units, concomitant contribution from synergistic and antagonistic muscles and metabolic fatigue related events. For example, lactate that triggers muscular adaptation. (14)
- Less efficient with respect to work per unit of time.
Extra-rest cluster training might be less efficient compared to longer sets with respect to work per unit of time. These point to the need for making rest periods the shortest duration needed in order to maintain the load and/or velocity. (3)
SECTION 4
Tactic #2: Drop Sets
‘Right now I could do more.’
What is the definition of drop sets?
With drop sets, the load is reduced within a set. Additionally, the exercise can be changed within a set, a strategy that is termed mechanical drop sets. Thus, drop sets are a form of Cluster Training where intra-set rest-periods are used to reduce the load used.
What is the purpose of drop sets?
A drop set is the tactic used to execute the strategy of matching the load to the capacity of the athlete-client as closely as possible, repetition by repetition, throughout a set. (See above.) As strength drops throughout the set, the load is reduced or there is a switch to a stronger range, position or contraction type.
Conceptually, two types of drop sets can be described: (23)
- A higher load is used from the beginning of a longer set (of more than 1 rep).
- Additionally, repetitions are performed at the end of a set.
If – for example – the goal is to perform 6 repetitions with a 6RM load, then the athlete-client could have a higher load on each of the first repetitions of that set. Thus, there is a gap between the force that is produced and the force that could have been produced. Beginning with a higher load and reduced, the load gradually closes that gap.
After performing a set of 6 repetitions with a 6RM load, the athlete-client can no longer lift a 6RM load. However, the athlete-client could perform additional repetitions with a lower load. Such a strategy is also termed multi-poundage training or break down training. (24)
Thus, the application of drop sets centers around the question: Why would you lift less than you could have at any point in time? In the same non-technical vein, drop sets relate to the statement – I could do more right now.
4a. What are the Benefits of Drop Sets?
The examples above illustrate that drop sets theoretically could result in a
- higher average load
- higher # of repetitions
- higher volume load
across one set and, thus, effectively stimulate strength, hypertrophy and muscular endurance.
Below is a brief overview of research findings on drop sets:
- Drop Sets that begin with a heavier load may the increase the firing rate of motor units and recruit high threshold motor units. (20)
- Drop sets may promote a higher total workload and subsequently increased mechanical and metabolic stress. (19, 21)
- Drop sets may result in greater hypertrophy compared to traditional training. (21) However, when volume and intensity are equated, there is no difference in strength or hypertrophy gains between traditional sets or drop sets. (16,17)
- Drop sets may result in lower RPE and similar strength and size gains for similar volume of training. (16)
Thus, the most prominent take-home message is that the power of drop sets lays not so much in the structure of gradually reducing the load. The power of drop sets lies in the possibility of using a higher average load and achieving a higher number of repetitions and volume load.
We will continue this discussion of Cluster Training in Part 2 of this piece.
Karsten Jensen has helped world class and Olympic athletes from 26 sports disciplines since 1993. Many of his athletes have won Olympic medals, European Championships, World Championships and ATP Tournaments.
Karsten is the first strength coach to create a complete system of periodization, The Flexible Periodization Method – the first complete method of periodization dedicated to holistic, individualized and periodized (H.I.P) training programs.
Karsten shares all aspects of The Flexible Periodization Method (FPM) with his fellow strength coaches and personal trainers through The Flexible Periodization Method workshop series (Levels I-VIII). Find more information at www.yestostrength.com.