December 15, 2021

Exercise Periodization & the Principles of Variation


The principle of variation is often thought to be required to facilitate continued adaptation. In practice, we apply this principle through periodization. Broadly speaking, periodization can be defined as a systematic method of manipulating any of the acute training variables over time.

These acute training variables include:

  • Volume
  • Intensity (e.g.% of 1RM or RPE, respectively)
  • Frequency
  • Tempo
  • Rest periods
  • Range of motion
  • Exercise selection
  • Exercise sequencing

The predominant form of periodization that we see both in the literature and in practice involves manipulating the load being used. This is likely because the concept was originally designed to optimize a yearly plan for performance-based or strength athletes. Realistically, any of these variables can be periodized in a viable way.


Unfortunately, the research we have on periodization and hypertrophy is incomplete for many reasons (i.e., study design, duration, realistic rates of adaptation, etc.). Looking at the data that we do have, when comparing a ‘periodized’ plan to a ‘non-periodized’ plan, we don’t see much difference in hypertrophy (25). However, we can logically see that the design of these studies (i.e., the training protocol) is responsible for the outcomes – the primary variable manipulated was load (or rep range). Other data suggest that (at least in the short term) hypertrophy is equivocal regardless of the rep ranges used so long as each set is taken to a sufficient proximity to failure (10, 11).

On a related note, researchers have thoroughly investigated the individual effects of the acute training variables on muscle hypertrophy. We consistently see: benefits of using a full range of motion (19, 20), similar growth using various rep tempo schemes (17), and shorter rest periods negatively impacting performance and adaptation (18). However, the research on volume, intensity, and frequency is far more complicated. To keep things brief, a range of different weekly set volumes (12, 13, 14), intensities (10, 11), and frequencies (15, 16) have been found to be effective. This is likely due to the interdependent relationship these three variables share with one another, which is often misrepresented in the literature.

If hypertrophy is the goal, what do we periodize then? Practically, it doesn’t make much sense to adjust rep tempo or range of motion. Using a full range of motion (that’s within your structural capability) is almost always more effective than not. Adjusting rep tempo (in an attempt to maximize time under tension) usually requires a load or rep reduction, and in most cases, the resulting TUT is effectively the same. A case could be made for manipulating rest periods in the form of rest-pause training, but not for traditional straight sets – if rest periods between sets are reduced, you will need to do more sets (23). Manipulating set volumes and frequencies can be problematic for many reasons – primarily due to recovery rates and the mechanisms of fitness and fatigue. So that narrows things down to loading (which we already addressed), exercise selection, and exercise sequencing.


In practice, most high level bodybuilders don’t periodize their training (not in the traditional sense at least). Usually, physique athletes tend to operate on the microcycle (weekly) level – they manipulate exercise selection, exercise variety (from session to session), and the sequencing of those sessions. Let’s not forget the importance of real world observation in science. Observing something in practice leads to the generation of a hypothesis which sets the groundwork for tomorrow’s publications. Exercise selection (and variety) in many ways is still an area that needs more research. However, we do have some key studies that are worth looking at.

A 2014 study by Fonseca and colleagues examined how varying exercises and varying intensities (loading) would affect changes in muscle cross-sectional area (CSA) and maximal strength. They divided 49 subjects into five different conditions:

  • Constant intensity and constant exercise (CICE)
  • Constant intensity and varied exercise (CIVE)
  • Varied intensity and constant exercise (VICE)
  • Varied intensity and varied exercise (VIVE)
  • Control group (C)

The group names are self-explanatory. Two groups varied the load they used, two groups varied the exercises performed, and one group varied both load and exercise selection. The training protocol can be seen below:

At pre- and post-intervention, they measured cross-sectional area (CSA) of the whole quadriceps muscle and each of the individual heads. They also tested Squat 1RM. Following 12 weeks of training, they reported whole muscle CSA increased significantly in all experimental conditions, however, the groups who had a greater variety of exercises (CIVE & VIVE) presented significant hypertrophy in all of the quadriceps heads, whereas the CICE and VICE did not present significant hypertrophy in the vastus medialis and rectus femoris. Additionally, the CIVE group demonstrated greater strength increases than the other groups (see tables below).

Whole muscle:

Regional hypertrophy:

The authors of the paper suggested that different movements may result in different activation patterns of the individual heads. (More on this to come)

A similar and more recent, 2021 study done by de Vasconcelos Costa and colleagues investigated how varying exercises throughout a training week would impact growth across the entire muscle length. Over the course of 9 weeks, they randomized 22 subjects into two conditions:

  • A group performing the same exercises 3x/week
  • A group performing different exercises in each of the 3 sessions (i.e., A, B, C sessions)

Below is a figure of the protocol:

The primary variable assessed was muscle thickness (MT) using an ultrasound. Pre- and post-intervention, they took measurements at three sites (proximal, middle, distal) for the lateral and anterior thigh, the biceps, and the triceps.

In a similar manner to the Fonseca study, they observed a “main time effect” in both conditions (just a fancy statistical term indicating both groups experienced significant growth from pre to post). However, the group with a greater variety of exercises saw growth at every measurement site whereas the lower variety group saw growth at most sites, but not all.

Below is a figure displaying MT measurements, the change from pre to post, and statistical analysis:

It would be interesting to see this study replicated with a modified exercise selection. Considering the biceps showed a significant difference between groups, this likely resulted from the study’s design. In each of the three sessions, bicep curl variations were performed at different degrees of shoulder flexion/extension which changes the muscle’s length considerably (being a biarticular muscle). We also know from previous data that a variation in muscle length alters the tension placed on a muscle due to “active insufficiency” (24). The variation here is much more substantial than other muscle groups (i.e., a hack squat and a barbell squat are much more similar), so perhaps the differences found would be greater if they followed a similar pattern of exercise selection for other muscle groups.


The authors in both papers speculated their findings could potentially be explained by three primary factors: muscle morphology, joint positioning, and range of motion. In order to understand how these factors are influencing adaptation, we need to be familiar with two important principles: the force-velocity relationship and the length-tension relationship.

The force-velocity relationship demonstrates the inverse relationship between a muscle’s shortening speed and the force applied. By definition, it explains how much mechanical tension  is placed on a given muscle fiber. As force demands increase, rep speed slows down – a slower muscle shortening speed means a greater tension stimulus (which is why the latter reps of a set are so important for muscle growth). In conjunction, a muscle’s ability to produce force is influenced by its length (defined as the length-tension relationship). From a structural standpoint, this is important. Several muscles in the body are “compartmentalized,” meaning they are composed of multiple divisions with different origin and insertion points (7). It’s common for some divisions of the same muscle to have different architecture (different fiber orientations, different lines of pull, etc.) so it’s likely that each region will work harder at specific portions of the range motion (9).

Research on regional hypertrophy supports this idea: two studies utilizing the leg extension demonstrated greater CSA increase in the distal portions of the vastus lateralis and rectus femoris (4, 5). However, other (more proximal) regions of the quad seem to be favored in a squat pattern (6, 8). We also seem to see a similar pattern with other muscle groups. A 2020 study on triceps training reported that performing the bench press produced greater growth in the lateral head of the triceps, while the triceps extension produced greater growth in the long and medial heads (3).


For late-stage intermediates and advanced athletes, providing some sort of variation in training stimulus will be required at some point. However, the type and amount of variation required needs to be specific to the type of athlete. For hypertrophy training, a variation in rep ranges may not necessarily provide a different growth stimulus – for reasons mentioned above and in previous articles. A high tension stimulus, both in magnitude and duration, training high-threshold motor units is what initiates the cascade of events resulting in the adaptation we’re looking for. Manipulating rep ranges/loading just determines when those high-threshold motor units are recruited in a set. Some will argue that a lighter or heavier load will preferentially train fast or slow twitch fibers, but this hasn’t been observed in the literature (21).

Strategic/systematic changes in exercise selection and intra-session structure (e.g. exercise sequence) may be an effective method of periodization for the goal of muscle hypertrophy. As a muscle often has more than one function, exercise variety clearly matters when looking to achieve maximum ‘uniform’ hypertrophy. So how can we apply this? Well, having some degree of variety within a session is clearly beneficial (as practitioners, we all know this). Within a training week, this might mean keeping a similar session structure with sets, rep range, proximity to failure, etc. but undulating the exercises done like the de Vasconcelos Costa study. Now, this isn’t saying you should change exercises every single session. It’s a balancing act – you may benefit from having a greater variety of movements, but there has to be some sort of consistency (the subjects in each study mentioned were still performing their weekly plan/exercises week after week for the duration of the study). Greater exercise variety can mean less frequent ‘practice’ at the movement, and we know that some degree of skill competency (a neurological adaptation) is necessary, even with the goal of muscle growth (22). The amount of practice will depend on someone’s level of advancement and how familiar they are with the movement.

Organizing your training in this way can promote greater recovery in the short-term as well. If the stimulus provided targets specific regions or “compartments” of a muscle, then muscle damage will follow this non-uniform pattern. With the influence muscle damage can have on motor unit recruitment, anything that reduces the amount of unnecessary muscle damage is a good thing. Having a variety of movements that challenge the muscle in a unique way increases a program’s “efficiency” by reducing overlap (i.e., we get a more complete stimulus with the same set volume). This could mean undulating your training directed at specific regions and/or specific muscle lengths on a daily (DUP), weekly (WUP), or even monthly (block) basis.

There’s an endless amount of ways to apply this, and from a physiological standpoint, this is the type of periodization that makes the most sense.


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Josh Bradshaw, MS