Throughout my career it has seemed obvious to me that principles of periodization must be applied if we want to create result-producing, long-term training programs. Therefore, I have always been excited to learn as much as I can about periodization and I expected strength coaches and personal trainers to be excited when I released The Flexible Periodization Method in 2010.

It was a surprise to me that the attitude and perception towards periodization was mainly negative for a variety of almost opposite reasons. On strength coach forums, articles and through communication with coaches I read and heard that periodization is:

  • Too rigid
  • Too complicated
  • Too time consuming
  • Not scientifically proven

Additionally, many coaches are tired of the discussion about which periodization system is best.

For the above reasons, many coaches turn away from periodization. This is problematic because research indicates that to achieve optimal results with training programs that are longer than four weeks, principles of periodization must be applied. (1)

The above critique is largely based on looking on the examples how periodization has been applied, for example in the eastern bloc decades ago.

This article looks at the various examples of periodization (the well-known systems) and extracts various elements of these systems. This article demonstrates how these elements are principles (or strategies) that can be used freely, not bound to a particular system.

What is the definition of periodization?

The non-technical definition, according to the dictionary, is that periodization is a division into periods.

With the Flexible Periodization Method (FPM), the technical definition of periodization is a division of a longer training cycle into periods with different goals, structures and content of the training program. These periods, with different goals, different structures and different content are sequenced in such a way that selected physical abilities are maximized at the goal attainment date. (2)

RELATED: The Flexible Periodization Method: The Decision-Making Process

With the above definition, periodization is a strategy or principle for organizing long term training. The strategy, on a basic level, is to divide the longer period into smaller periods with different goals, structures, and content of the training program.

Thus, if you ever make ANY changes to the training program, you have a new period with (at a minimum) a content and structure of the training program. As a result, you are applying periodization as a strategy.

Thus, while we as coaches and trainers can avoid any one of the named systems of periodization (see below) it is virtually impossible to avoid applying periodization as a strategy. 

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What are the key arguments that support the use of periodization?

As mentioned above, research indicates that principles of periodization must be applied to see maximal progress in programs that are longer than four weeks in duration. However, some authorities don’t agree with that conclusion and find that the studies mainly prove that variation is important. (3)

What should coaches expect from the scientific method in terms of a proof of periodization?

One of my former professors stated that, “Training is not science, but science can enhance training” (Dr Jens Bangsbo, University of Copenhagen). The scientific method involves change one variable at a time. (4) In contrast, real life periodization involves multiple variables at the same time and very often the relationships between these variables change from athlete to athlete. In conclusion, it is my opinion we as strength coaches should look for and use proof of elements of periodization, not proof of periodization as a whole.

Below is a very brief review of some of the additional arguments that support periodization as a strategy.

The Principle of Accommodation

The Principle of Accommodation, often considered a general law in biology, states that the response of a biological object to a constant stimulus decreases over time. (5) In the case of strength and conditioning or fitness training, the “biological object” is the human mind-body and the stimulus is the training load.

The Principle of Accommodation explains why there is no ‘best” program. After a relatively short period of time (practices) the athlete accommodates to the program and reaches a plateau.

To stimulate new progress one or more program variables must be changed. Thus, the result is a new period with new content and structure of the training.

General Adaptation Syndrome

Canadian biologist, Hans Selye, coined the term General Adaptation Syndrome (GAS) to describe how the adrenal glands respond to an initial alarm reaction followed by a reduction of an organism’s function in reaction to a noxious stimulus. The key to the continued adaptation to the stress is the timely removal of the stimulus so that the organism’s function can recover. (6)

The general adaptation syndrome states that the body will go through three stages in its response to a new and stronger stress: the alarm stage, the resistance stage, and the exhaustion stage.

The optimal exploitation of the body’s stress response can be described as follows:

  1. The new training stimulus should be strong enough to initiate the alarm stage.
  2. The training stimulus should be applied repeatedly (including progressive overload) throughout the resistance stage.
  3. Finally, the training stimulus should be removed in the beginning of or somewhat into the exhaustion stage.

In conclusion, the General Adaptation Syndrome shows us points of in the direction of a division of a longer training cycle into periods with a developmental training load, alternated with periods with a reduced training load that allow the body to recover.


Sequences, Synergy and Incompatibility

By utilizing the definition of periodization as, “different periods with different goals, structures and content of the training program," periodization of a particular form of training is supported if one or more of the following scenarios are true:

  • The development of specific, relevant physical qualities may happen safer and more effectively when other specific physical qualities are developed first.

Example: Flexibility before strength, speed, power or endurance. (7)

  • There is synergy between the development of two specific qualities: There should be a period where these two qualities are trained together.

Example: A heavy lift before a power movement enhances the power output. (8)

  • If there is incompatibility between two specific physical qualities: the training of these two qualities should be separated in different periods.

Example: High Intensity aerobic and high intensity anaerobic training. (9)

Stop looking for the best system of periodization and focus on this instead.

Due to the nature of the scientific method and our (coaches) desire to give our athletes the best possible programs, there is a lot of focus on which periodization system is “best."

In a book commissioned by the Danish Sport Federation (my native country) I reviewed a lot of the literature on linear periodization, reverse linear periodization, daily undulating periodization, conjugate periodization, and block periodization with the purpose of figuring out which system is best.

Many studies show differences in effectiveness between different periodization systems. (10) In contrast, some large reviews show no difference in effectiveness between linear and nonlinear periodization. (11) A major reason that the results regarding the best periodization system is inconclusive is that the effect of a particular periodization model depends on what training the participants previously performed leading up to the study.

MORE: The Flexible Periodization Method: Out of Sight, Out of Mind?

Rather than focusing on which system is best, the process of writing the mentioned book led me to believe that we are much better served by understanding and extract the essential elements of periodization systems and how they are used differently in the different examples of periodization. As these elements are extracted they appear as flexible strategies that can be used freely based on the needs of your athletes

For the case of brevity additional references for the following section is limited. References available upon request.

1. Does the system incorporate a parallel or sequential development of physical abilities?

Based on the periodization literature, sequential development of physical abilities is the case when up to three physical abilities are trained with developmental loads within the same mesocycles. Parallel development of physical abilities is the case when 4-6 physical abilities are trained with developmental loads within the same mesocycles. (12)

Parallel development is considered ideal for beginners that need multilateral development and who makes progress despite relatively low volume on any physical capacity. Additionally, parallel development is also considered an option when preparation periods are short.

Sequential development is used for more advanced athletes that need to direct more energy and time towards each selected physical ability. Additionally, sequential development of physical abilities comes into play when the number of decisive physical abilities exceeds the number of abilities that can be simultaneously developed.


2. How does the system make use of variation and contrast?

Daily undulating periodization applies a lot of variation WITHIN one week of training, but limited variation across weeks.

Linear periodization, conjugate periodization, and block periodization apply less variation within a training week, but substantial variation from block to block (meso cycle).

When you consider variation within one week of training it is a key difference if you create variation WITHIN the same intensity zone or if you create variation by incorporating different intensity zones.

3. What is the pattern for change in volume and intensity?

Linear periodization involves a gradual decrease in volume with concomitant increase in intensity. This pattern is excellent for the development of maximal strength or hypertrophy.

Reverse linear periodization involves the opposite pattern: a gradual increase in volume with a gradual decrease in intensity. This pattern is excellent for the development of muscular endurance.

Another aspect of the pattern of change in volume and intensity is degree of change across the macro cycle. Two major patterns are described in the literature.

Concentrated loading: A concentration of the training load early in the macro cycle followed by recovery.

Distributed loading: A distribution of the training load throughout the macro cycle. Specifically, conjugated periodization describes a use of concentrated loading. (13)

Concentrated load is for athletes at the advanced level with no injuries, a high training capacity, and the time to double their regular training volume.

4. (How) is auto-regulation applied?

Auto-regulation in the training program means that the program can self-regulate based on the athlete's capacity on a given training day. Auto-regulation is essential to the ability to apply the correct amount of stress on a given day.

So-called Flexible Daily Undulating Periodization allows the athlete to choose between different intensity zones on a given training day based on their readiness. (14)

Block periodization claims that the relatively short training stages allow for accurate regulation of the training program in the next stage based on the results of the previous stage. (See reference 9)

Strategies for applying auto-regulation should in general ensure that the original target adaptations of the practice are maintained.


The application of principles of periodization is a must for success in long-term training. Understanding periodization as a principle with the potential use of several flexible strategies sets you free to apply periodization in a way that is suitable for the athletes that you work with.


  1. Fleck SJ, Kraemer WJ. Advanced Training Strategies. Designing Resistance Training Programs 3rd Ed. Chapter 7, p. 210. Human Kinetics; 2004.
  2. Jensen, K. Periodization Simplified: How To Use The Flexible Periodization Method on The Fly:  PRINCIPLE #1 Scientific studies and fundamental physiological models form the rationale for periodization. . 2015
  3. Kiely J. Periodization Paradigms in the 21st Century: Evidence Led or Tradition Driven. Int J Sports Phys and Perf. 7: 242-250. 2012.
  5. Zatsiorsky W. Basic Concepts of Training Theory. Science and Practice of Strength Training. Chapter 1, p. 5. Human Kinetics; 2006.
  6. Kraemer WJ. Vingren JL, Spiering BA. Endocrine Responses to Resistance Exercises. Essentials of Strength Training and Conditioning 3rd Ed. Chapter 3, p. 42. Human Kinetics; 2008
  7. Jensen, K. Principle #5: First develop flexibility, AND THEN develop strength, speed, power or endurance. Periodization Simplified: How To Use The Flexible Periodization Method on The Fly. Page 28-34. 2015.
  8. Duthie GM, Young WB, Aitken DA. The acute effects of heavy loads on jump squat performance: an evaluation of the complex and contrast methods of power development. J Strength Cond Res.  16(4): 530-538. 2002
  9. Issurin W. Microcycles, mesocycles and training stages. Block Periodization. Breakthrough in Sport Training. Chapter 3, p. 78-128. Ultimate Athlete Concepts. 2008.
  10. Jensen K. Essential characteristics of Periodization Systems. Performance Optimization With Periodization. Chapter 3, page 40-57. 2013 (in Danish)
  11. Harries SK1, Lubans DR, Callister R. Systematic review and meta-analysis of linear and undulating periodized resistance training programs on muscular strength. J Strength Cond Res.  Apr;29(4) 2015
  12. Jensen K. Principle # 15: The Flexible Periodization Method integrates Sequential and Parallel Development of Physical Abilities. Periodization Simplified: How To Use The Flexible Periodization Method on The Fly. Page 75-81. 2015
  13. Siff M. Organization of Training. Supertraining, 6th ed. Chapter 6, p. 347. Supertraining Institute; 2004.
  14. McNamara JM, Stearne DJ. Flexible NonLinear Periodization In A Beginner College Weight Training Class. J. Strength Cond Res: 24(1): 17-22. 2010

Karsten Jensen, MSc Exercise Physiology, has helped world class and Olympic athletes from 26 different sports for over 20 years. 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 with his fellow strength coaches and personal trainers through The Flexible Periodization Method Certification (Level I-IV).