Periodization is often claimed to be an important feature of strength training programs for producing hypertrophy. On the other hand, some researchers have noted that the evidence in favor of periodized programs is quite weak, and they argue that the underlying biological rationale for periodization is not very convincing.
So is periodization actually useful when training for hypertrophy, and if so, how should we use it?
What is periodization?
Periodization is difficult to define, and has become controversial in recent years. Many researchers and coaches have proposed definitions, but since no single definition has attracted widespread adoption, it remains in use in different ways by different people.
Ultimately, however, periodization is just a tool for providing variety within a strength training program.
Variety is a key strength and conditioning principle (like progressive overload, specificity, and individuality) and periodization allows us to apply variety to a program in a structured (and hopefully also useful) way.
Periodization has been investigated by researchers almost exclusively by changing the repetition range (percentage of one repetition-maximum) used from one workout to the next. We can call this “load periodization” to differentiate it from changing other training variables, such as volume (number of sets), rest period duration, tempo, contraction mode, range of motion, or exercise. Even so, the overall term “periodization” refers to changing any of these training variables, often at the same time.
Periodization of various training variables has been proposed to cause (1) larger improvement in muscular performance (or in the case of bodybuilding, greater muscle growth), and (2) a reduction in the risk of non-functional overreaching or overtraining.
Let’s take a look at each of those possible benefits.
How could load periodization enhance muscle growth?
Load periodization has been proposed to enhance hypertrophy in at least three completely different ways: (1) fiber type-specific hypertrophy when training with different loads, (2) muscle-specific hypertrophy when training with different loads in multi-joint exercises, and (3) improvements in work capacity.
#1. Fiber type-specific hypertrophy
Some researchers believe that different repetition ranges (loads) produce hypertrophy of the muscle fibers controlled by different motor units.
They suggest that training with heavy loads preferentially increases the size of the (mainly fast twitch) muscle fibers controlled by high-threshold motor units, while training with light loads preferentially increases the size of the (mainly slow twitch) muscle fibers controlled by low-threshold motor units, because of the longer period of time for which these muscle fibers are exposed to the strength training stimulus.
However, there is little evidence to support this hypothesis. What is more, the underlying biological rationale is shaky for two reasons.
Secondly, there is no good reason to believe that the muscle fibers of low-threshold motor units actually grow after strength training. Indeed, if the earlier reps of a set with light loads to failure did contribute meaningfully to overall hypertrophy, then training with light loads while avoiding failure would cause meaningful muscle growth (it doesn’t), aerobic exercise would cause meaningful muscle growth (it doesn’t) and slow tempos would produce more hypertrophy than fast tempos when using light loads (they don’t), because the fast tempo would prevent mechanical loading of the muscle fibers of low-threshold motor units from occurring in the early reps, while the slow tempo would involve high forces of the working muscle fibers.
#2. Muscle-specific hypertrophy in multi-joint exercises
When we perform a multi-joint exercise, we tend to assume that the contribution of each prime mover muscle is the same, regardless of the load on the bar. However, this is not the case.
In fact, during many multi-joint exercises, the load on the bar affects which muscle group or groups are working hardest. For example, as load increases in the bench press, the triceps brachii (and possibly also the sternocostal head of the pectoralis major) increase their proportional contributions. Similar effects occur during many lower body movements, including the squat, deadlift, and forward and lateral lunges.
Consequently, using a range of loads during multi-joint exercises could be an effective strategy for producing greater hypertrophy across all of the prime movers involved in an exercise.
#3. Improvements in work capacity
Training with light loads allows greater increases in volume load to occur than similar numbers of sets with heavy loads. This may enhance work capacity for future training blocks.
In turn, this increased work capacity may allow lifters to perform greater volumes of training, and thereby accelerate their rate of muscle growth, since training volume seems to be quite closely linked to hypertrophy.
However, this measure of volume that is improved by training with light loads refers to volume load (sets x reps x weight) and it is not the same measure of volume that has been linked to greater hypertrophy (the number of sets to failure). It is unclear whether increasing the ability to perform greater volume loads (sets x reps x weight) also increases the ability to withstand a greater number of sets to failure without either reaching a plateau or decreasing the rate of gains.
How could periodizing other training variables enhance muscle growth?
Periodizing other training variables may also be beneficial for maximizing muscle growth, because of regional hypertrophy. Different exercises, ranges of motion, and contraction modes all produce muscle growth in different regions of the same muscle.
Regional hypertrophy probably happens for two main reasons. It could occur either (1) because of differences in the amount that the muscle fibers increase in length or diameter after strength training, or (2) because of differences in the growth of different functional compartments.
Different exercises most likely produce hypertrophy in different regions of a muscle due to forces being exerted in slightly different directions at a joint, whereas different contraction modes and ranges of motion likely produce hypertrophy in different regions of a muscle.
Eccentric training and larger ranges of motion tend to cause greater increases in muscle fiber length, while concentric training and partial ranges of motion tend to cause greater increases in muscle fiber diameter. Increases in muscle fiber length tend to be associated with greater gains in the distal region of a muscle, while increases in muscle fiber diameter tend to be associated with greater gains in the middle region.
In general, eccentric training and concentric training produce similar overall muscle growth, but the region differs. Similarly, contrary to popular belief, full and partial ranges of motion probably also cause similar overall muscle growth, but again the region and type of growth differs.
Can periodization reduce the risk of non-functional overreaching and overtraining?
In general, the risk of non-functional overreaching and overtraining is often discussed in the context of the general adaptation syndrome. However, this syndrome ultimately refers to the amount of muscle damage that is incurred, which makes variety (and periodization) a tool for managing this problem.
Non-functional overreaching happens when we train and yet do not achieve any gains in our desired outcome at either the end of the training program, or after a taper. Overtraining is a medically-diagnosed condition that involves reduced performance over a longer period of time (and possibly muscle loss). In practice, most people are referring to non-functional overreaching when they say overtraining.
Most of the time, non-functional overreaching is measured by reference to performance outcomes such as maximum strength. It seems to happen when a subsequent workout is performed while muscle damage is still present from a previous workout, which prevents progressive overload from being achieved, and may lead to reduced performance. This muscle damage may also prevent neural and local muscular adaptations from occurring, if the muscle damage leads to central nervous system fatigue, thereby stopping full motor unit recruitment from being reached in the subsequent workout.
When training for hypertrophy, non-functional overreaching would strictly refer to a cessation in gains in muscle size, which is very difficult to measure. This could occur with or without a similar cessation of gains in repetition strength (as measured by workout performance) or in maximum strength. Even so, assuming that repetition strength (workout performance) is a valid indicator of muscle growth, periodizing some variables may help reduce the risk of non-functional overreaching and overtraining by managing the amount of muscle damage that occurs.
When we alter either the exercise, contraction mode, or range of motion, we alter the region of the muscle that experiences the greatest activation in its motor units, and also the region that experiences the greatest mechanical loading, which leads to muscle damage. Consequently, rotating between these factors could allow us to train a muscle more frequently, since different regions of a muscle would be damaged by each exercise, contraction mode, or range of motion. Similarly, when we alter the load in a multi-joint exercise, we could shift the amount of muscle damage that each of the prime movers experiences.
On the other hand, if we are aiming to keep training volumes high (in order to maximize hypertrophy), then load periodization is unlikely to have the benefit that it has during strength training programs for athletes. In such training programs, increases in load occur in tandem with decreases in volume, and this reduces muscle damage. Consequently, load periodization is likely to have beneficial effects on the risk of non-functional overreaching only in multi-joint exercises.
Do we need to use periodization to implement the principle of variety?
It is worth noting that all of the benefits that are observed from periodization can be similarly achieved by other methods of delivering greater variety, so long as the variety is sufficient to achieve the same goals.
Certain other ways of providing variety can be superior to periodization, because they allow adaptations to follow their natural course, rather than predicting how they will occur in advance.
For example, one popular method for varying exercises during bodybuilding programs is to continue using an exercise for a muscle group until progressive overload stops. This very simple method ensures that progress always continues, and that exercises are only varied when absolutely necessary, which prevents variety from being implemented for the sake of it, instead of for a specific purpose.
What are the practical implications?
There are very good reasons to vary exercises, contraction modes, and ranges of motion during strength training, as well as load in multi-joint exercises. Varying these training variables will likely reduce the risk of non-functional overreaching and enhance muscle growth. On the other hand, the rationale for varying loads during single-joint exercises is much weaker.
In practice, the best way to vary exercises, contraction modes, and ranges of motion (and load during multi-joint exercises) within a periodization model for bodybuilding is to use A and B workouts for each muscle group.
Essentially, this is daily (or weekly) undulating periodization (depending on your workout frequency). If you train each muscle group twice each week, you can use a different exercise, contraction mode, or ranges of motion (or load in multi-joint exercises) in each workout. If you train each muscle group once each week, you can use a different exercise, contraction mode, or ranges of motion (or load in multi-joint exercises) every other week.
When varying contraction mode, you can use conventional stretch-shortening cycle training instead of concentric-only training, and eccentric overload instead of eccentric-only training. This is slightly less specific than using concentric-only and eccentric-only training, but will still produce some differences in regional hypertrophy and is much easier to do in practice.
What is the takeaway?
Periodization is a tool for providing variety within a strength training program. Periodizing load may be helpful when training for hypertrophy using multi-joint exercises, but otherwise the benefits seem to be limited. In contrast, periodizing exercise, contraction mode, and range of motion may all enhance muscle growth through regional hypertrophy, and could also help prevent non-functional overreaching by changing the region of the muscle that experiences muscle damage.