An Introduction to Loading: Foundation & Principles

The APTA recently joined the Choosing Wisely® initiative and published a list of 5 treatments that do not reflect current best practice. One of those was sub optimal loading of resistance exercise in older populations. The point made regarding the need for adequately dosed exercise among seniors is an important one, however it isn’t limited to that population. Strength training is one of the more powerful tools available to the therapist, and when applied thoughtfully and appropriately, it plays a significant role in the rehabilitation process. A previous post of mine discussed applying clinical decision making to exercise prescription. The goal of this post is to expand on this idea by discussing strength training in particular through a review of basic principles and the introduction of autoregulatory periodization. This will be done in two parts. Part I will look at the components of strength training and introduce the idea of autoregulatory periodization. In part II the focus will be practical clinical application of these concepts.

Physical therapy is defining itself around movement, and therapists are increasingly identifying themselves as movement practitioners. Because of this, an understanding of motor control should influence our clinical decision-making. A constraints-based view of movement allows us to discuss movement as emerging from the interaction of three major constraints:

  1. The environment
  2. The task
  3. The individual

Physical therapy is defining itself around movement, and therapists are increasingly identifying themselves as movement practitioners..

What this means is that changes in any of these three areas will potentially influence the way the individual moves. Strength training is an intervention directed at manipulating the constraints of the individual. With increased strength and/or capacity, the organism has more options available when faced with performing a task. Movement issues that are related to weakness or decreased capacity can thus be addressed by increasing the organism’s capacity. In situations such as fatigue or poor control, increased physical capacity may even act as a buffer and help the individual maintain movement options. In this model of thought, the strength training is performed with the assumption that manipulation of the individual’s constraints will lead to a shift in the output (movement) towards a more optimal expression.

Background Concepts

There are three basic training principles that must be manipulated in order to drive adaptation:

  • Overload
  • Variation
  • Specificity

The closest thing to “functional training” that exists outside of performing the specific task or sport is probably training that reflects the bioenergetic demands of a task while using movements with mechanical specificity.

  1. Overload

Overload is described as “a stimulus of sufficient strength, duration, and frequency [such] that it forces an organism to adapt.”1 This can be tracked in a variety of ways. One of the better estimates of work accomplished is the volume load (repetitions x weight lifted) which gives a simple number that can be tracked across time. While useful, this is often impractical to apply in a busy clinical setting. Alternatively, a measure of the Rating of Perceived Exertion (RPE) has been shown to be a reliable measure of exercise intensity.2 RPE provides a very practical method of measuring session intensity, and when combined with an auto-regulatory training approach it creates a flexible method of exercise prescription that reflects the individual’s readiness to train.

  1. Variation

Variation describes the manipulation of training variables, which results in changes in the overload stimulus. Training at different rep ranges or zones is one way to address this principal.

  1. Specificity

The last one, specificity, is often confused with “functional” type training. This is incorrect. Specificity can be approached from two main perspectives: a bioenergetics and/or a mechanical one. Siff and Verkoshansky list out a number of considerations that must be identified when addressing mechanical specificity.1 These include looking at the movement’s amplitude and direction, the dynamics of the effort, the rates of force development, and contraction types. When viewed from a bioenergetics perspective, a task analysis must be done initially. Once a breakdown of the energy system demands has been identified they can be reflected in the training.

Each of the three energy systems can be viewed along a continuum of power to capacity, and training should reflect this. For instance, training for maximal vertical jump (anaerobic power emphasis) will require a very different approach than training for a marathon (aerobic capacity emphasis). Patrick Ward has a great post on this thought process that should be read by anyone looking to learn more about it. The closest thing to “functional training” that exists outside of performing the specific task or sport is probably training that reflects the bioenergetic demands of a task while using movements with mechanical specificity. These basic principals are foundational to understanding exercise prescription.

Autoregulatory Periodization

By this point, it’s obvious that the manipulation of variables in exercise prescription encompasses more than merely assigning sets and reps. Exercise prescription begins with clinical decision-making. Asking the right questions (what adaptations are required?) drives the answers (the methods used to elicit these adaptations).

This can become challenging since we deal with patients who have many conflicting demands outside of the clinic. Since the stimulus is what drives the organism to adapt, it’s important to adhere to a consistent approach. This will ensure that inputs are consistent with the desired outcomes. At the same time, the readiness of the patient – defined as the individual’s ability to perform at any given moment – must also be taken into consideration. Basic biomotor abilities will ultimately determine the limits of readiness, but day-to-day stressors will constrain it to a large extent as well. Any changes in stressors outside the clinic will require adaptations in even the most well written program to reflect the patient’s current state of readiness. Because of this, a method of programming that is modifiable based on relevant feedback is important. This is where the idea of autoregulatory training seems to come in.

Mel Siff described this concept in his book Supertraining in which he took the daily adjusted progressive resistive exercise (DAPRE) system and modified it to allow for more flexibility in its application.3 This modified protocol is a zone-based approach built around strength/power, strength/hypertrophy, and hypertrophy focuses. The original protocol that Knight developed, the DAPRE system, was designed so clinicians could prescribe exercise that took the patient to a maximal effort.4 Siff took this further with a focus on zones that addressed a particular emphasis.

The basic concept of APRE as described by Siff involved selecting a rep range based on goals. The classic phases are:

  • 3 RM phase
  • 6RM phase
  • 10RM phase

The load was based on a previously determined rep max and the first three sets follow a classic approach of:

  • 50% of the rep max for the first set
  • 75% of the rep max for set 2 and
  • 100% of the rep max for set three taken to failure

At this point, the number of reps achieved on the third set determines the weight lifted for the fourth and final set. If the number of reps achieved was within 1 of the goals either above or below, then the weight is left the same and the patient proceeds to perform his last set to failure as well. This last set is used to determine the next session’s rep max. The unique nature of APRE becomes apparent if more or less than the expected repetitions are performed. If the third set fell within 2-3 reps above or below the goal then the fourth set was increased or decreased by a modest amount. And if set 3 was 4+ reps above or below the weight on, set 4 was adjusted by a more significant amount. This has been applied successfully in a variety of settings and has been shown to actually outperform more standard methods of periodization in some cases.5

Applied as described above, this is an excellent approach to exercise prescription. However, I’ve found a few modifications allow for more clinical applicability. The main change is in the introduction of RPE to the program for measuring intensity. As usual, Mell Siff discussed this as well and termed the approach “cybernetic periodization” due to the use of feedback from the system’s output to dynamically modify input. There are many advantages that an approach like this provides:

  • Feedback like this allows the system to be somewhat self-regulating.
  • It also allows for monitoring the intensity without establishing a true rep max.
  • At time this can be very beneficial due to time constraints or lifting limitations due to stages of injury.
  • The desired RPE is determined by many of the previously discussed parameters and will therefor vary based on the goal of the session.
  • This adaptability allows for application of cybernetic periodization from early stage rehabilitation through return to sport.

Part 2 available soon will go over practical applications of these concepst – Originally published on Medbridge



  1. Cardinale M, Newton R, Nosaka K. Strength and Conditioning. Wiley; 2011.
  2. Day ML, McGuigan MR, Brice G, Foster C. Monitoring exercise intensity during resistance training using the session RPE scale. Journal of Strength and Conditioning Research. 2004;18(2):353–358. doi:10.1519/R-13113.1.
  3. Verkhoshansky YV, Siff MC. Supertraining.; 2009.
  4. Knight KL. Knee rehabilitation by the daily adjustable progressive resistive exercise technique. Am J Sports Med. 1979;7(6):336–337.
  5. Mann JB, Thyfault JP, Ivey PA, Sayers SP. The effect of autoregulatory progressive resistance exercise vs. linear periodization on strength improvement in college athletes. J Strength Cond Res. 2010;24(7):1718–1723. doi:10.1519/JSC.0b013e3181def4a6.
  7. Mitchell CJ, Churchward-Venne TA, West DWD, et al. Resistance exercise load does not determine training-mediated hypertrophic gains in young men. Journal of Applied Physiology. 2012;113(1):71–77. doi:10.1152/japplphysiol.00307.2012.
  8. Burd NA, Mitchell CJ, Churchward-Venne TA, Phillips SM. Bigger weights may not beget bigger muscles: evidence from acute muscle protein synthetic responses after resistance exercise. Appl Physiol Nutr Metab. 2012;37(3):551–554. doi:10.1139/h2012-022.
  9. Burd NA, West DWD, Staples AW, et al. Low-Load High Volume Resistance Exercise Stimulates Muscle Protein Synthesis More Than High-Load Low Volume Resistance Exercise in Young Men. Lucia A, ed. PLoS ONE. 2010;5(8):e12033. doi:10.1371/journal.pone.0012033.t003.
  10. Baechle T, Earle R. Essentials of Strength Training and Conditioning. 2nd ed. Human Kinetics Publishers; 2008.