What can the general adaptation syndrome tell us about periodization?
Open any textbook on strength training and you will find a description of Selye’s general adaptation syndrome, and its application to programming and (especially) periodization.
But is the general adaptation syndrome really applicable to strength training? And if so, how does it underpin our use of periodization?
These are important questions that need answers.
The generalized stress response — introduction
The General Adaptation Syndrome (GAS) was proposed by the researcher Hans Selye. Before forming this hypothetical framework, Selye carried out a number of experiments on rodents in which he exposed them to a variety of different hardships.
Selye discovered that while each unpleasant experience caused specific defence reactions in the mice, such as the release of specific antibodies or the compensatory growth of specific muscle groups, there was also a generalized stress response that was always the same.
In fact, Selye’s hypothesis should be called the “generalized stress response” because that is a more accurate description of what it describes.
This generalized stress response to a stressor was divided into three phases.
- Alarm reaction — involves the breakdown of body tissues (catabolism), hypoglycemia (low blood sugar), gastrointestinal ulcers, and swelling of the adrenal glands. More modern research tends to refer to the response in the hypothalamic-pituitary-adrenal (HPA) axis, including cortisol levels.
- Resistance — reverses the symptoms of the alarm reaction phase, and also creates adaptations that allow the subject to withstand higher levels of the imposed stressor.
- Exhaustion — reverts to similar symptoms as the alarm reaction phase.
Importantly, Selye was very clear that the generalized stress response was the sum of all stressors acting on an individual at any time.
Additionally, Selye noted that each stressor has specific effects that produce specific adaptations, and the nature of these specific adaptations influences the course of progress through the three phases of the GAS framework.
Let’s explore those two insights a bit further.
The generalized stress response — sum of stressors
When imposing a stressor on a subject, the generalized stress response is determined by the sum of all stressors acting at that time.
For example, when a rodent is subjected to a toxin, their generalized stress response to that toxin is determined not just by the amount of the toxin, but also by their living conditions, their ability to exercise, and many other factors.
In other words, being in what we might term a “stressful” environment reduces the ability of the mouse to overcome the stressor imposed by the toxin. This makes the duration of their resistance phase shorter, and reduces their capacity to adapt to the imposed stressor.
This observation led Selye to propose that each animal has a finite amount of “adaptation energy” that can be dedicated to resisting and overcoming all imposed stressors. When other stressors are low, we can enjoy a very long resistance phase in which to overcome the imposed target stressor. However, in a stressful environment, any additional stressor can quickly push us into the exhaustion phase.
The generalized stress response — the role of specific adaptations
When a stressor is imposed on an individual, it has specific effects that produce adaptations.
When discussing his issue, Selye noted that specific adaptations could include improved resistance to cold, the release of specific antibodies to combat certain specific pathogens, or the compensatory growth of specific muscle groups to withstand greater mechanical loads.
Whether these adaptations are produced has nothing to do with the GAS, but when they occur, they do influence the duration of the resistance phase.
For example, when the ability to resist cold is improved, then the mouse might withstand researchers subjecting it to low temperatures for longer. When antibodies are produced, it can withstand greater doses of the pathogen. When certain specific muscle groups increase in size, it can withstand greater mechanical loads.
In other words, when we adapt to the stressor, we can withstand a larger dose of the *same* stressor in the future.
The key point is that the adaptation is specific. Developing the ability to produce antibodies does not help an organism withstand cold temperatures, nor does it enhance the size of muscle groups.
How can the GAS be summarized?
Essentially, the GAS framework can be reduced to three key concepts:
- Subjects experience a generalized stress response to an unaccustomed stressor. When they are exposed to this stressor for a period of time, they develop specific adaptations to it, and become resistant to it. Consequently, their symptoms of stress reduce, and they develop the ability to tolerate greater doses of it.
- There is a finite amount of “adaptation energy” available for responding to stressors. Therefore, when the dose of a single stressor is increased beyond a certain point, the resistance phase ends, and the subject is exhausted. Also, when multiple stressors are imposed at the same time, it is the sum of all these stressors that determines the duration the resistance phase.
- Adaptations to stressors are specific, so exposure to one type of stressor does not confer resistance to another stressor. Yet, it is the presence of the adaptations that allow organisms to enter the resistance phase. If no adaptation was possible, then the organism would remain in the alarm phase perpetually.
Summarizing the GAS framework in this way allows us to see how it can be applied to strength training.
How might the GAS apply to strength training?
We can model strength training as a stressor within the GAS framework, if we identify muscle damage as the main result of the stressor.
From Selye’s point of view, this is completely appropriate, since his studies involved applying a toxic agent that caused harm to his experimental subjects, which later recovered and self-repaired the damaging effects.
It also makes sense from a practical perspective, since muscle damage is the main factor that determines how long it takes to recover from a workout, and is often caused by strength training. Other forms of fatigue (both central and peripheral) produce only very transitory effects lasting a few hours.
- Alarm reaction phase — unaccustomed strength training can cause muscle damage, which leads to a temporary loss in strength. Similarly, some types of workout cause elevations in cortisol, which is a major stress hormone, and indicates that the HPA axis has probably been activated. Yet, other types of workout cause no muscle damage or reductions in strength, and do not cause measurable cortisol responses.
- Resistance phase — it is well-known that strength training produces very specific adaptations, and these can help improve the ability to withstand future, larger doses of strength training. Additionally, the imposition of other stressors (such as psychological stress from adverse life events) does reduce the available adaptation energy, and increase the time taken to recover from a workout.
- Exhaustion phase — while the precise nature of overtraining is still poorly understood, it does seem to involve increases in muscle damage, and rodent studies have shown that excessive strength training volume and frequency can lead to muscle loss.
In summary, some types of unaccustomed strength training workouts do seem to cause a generalized stress response, as well as muscle damage. The muscle damage response disappears once specific adaptations to the particular type of workout are developed, and the capacity to recover may be limited by the presence of other stressors, such as adverse life events. Finally, if the imposed workout load is too high, muscle damage becomes excessive and muscle atrophy is observed.
Yet, as the above analysis reveals, not all types of strength training workout can be modeled in this way, as they do not produce muscle damage.
When might the GAS apply to strength training?
Muscle damage only arises after workouts involving either (1) high forces while the muscle is either lengthening or in a lengthened position, or (2) a high degree of fatigue. Moreover, muscle damage is always greater when the workout is unaccustomed, compared to when it has been done before.
Thus, workouts involving high volumes, high levels of fatigue, and high muscle forces tend to cause more muscle damage than workouts involving low volumes, low levels of fatigue, and low muscle forces.
Training programs using these types of workout are therefore most easy to model within the GAS framework, as are training programs that incorporate a great deal of variety.
High volume strength training workouts as performed by bodybuilders tend to produce a reliable cortisol response, and also create a large post-workout reduction in strength, which is the main way we determine whether muscle damage has occurred.
In contrast, power training with light loads and fast bar speeds (and any other type of training that does not cause muscle damage) never seems to act as a generalized stressor. This is probably because the fast bar speeds require muscle fibers to contract at fast speeds. Fast muscle fiber contraction velocities mean that fewer actin-myosin crossbridges can form, which means that the mechanical loading on the muscle fiber is low, and this reduces the chance of muscle damage.
And while accustomed (low volume) maximum strength workouts generally always produce some muscle damage, they do not also produce a reliable cortisol response. So low volume strength training for maximum strength may only be a very mild generalized stressor, and it may only become stressful when volume is increased. This would explain why some athletes find it perfectly feasible to perform daily 1RM strength training.
What does this mean for periodization?
Some researchers have noted that the applicability of the GAS framework to strength training is essential for periodization to be a valid tool.
In practice, periodization can be defined as “incorporating non-random, pre-planned, and timetabled variety into a workout program” and the intended purpose of periodization is to increase gains in performance, while limiting the risk of overtraining (the exhaustion phase).
Periodization can have an effect on recovery from strength training as modeled by the GAS framework in three ways.
#1. Limited exposure
To the extent that introducing variety with periodization involves limiting the time spent performing workouts that involve high levels of muscle damage, then this would reduce the risk of entering the exhaustion phase.
Most traditional periodization models involve sequential phases of training, either in blocks designed to improve a specific fitness characteristic (muscle size, maximum strength, or power) or with inversely varying volume and relative load, where volume is progressively reduced over the program and percentage of 1RM is increased.
Such traditional periodization models clearly isolate the high-volume workouts that cause the most muscle damage into a block at the beginning of the program, after which muscle damage (and therefore the generalized stressor) is smaller during the maximum strength training phase, and non-existent in any power training phase. So, as long as the initial phase is not too long, this works out reasonably well.
#2. More recovery time
To the extent that introducing variety with periodization involves moving workouts that involve high levels of muscle damage further away from one another, then this would allow more time for recovery from the muscle damage, and thereby reduce the size of the imposed generalized stressor.
Many popular undulating periodization models allow more recovery time between muscle-damaging workouts, by distributing the high-volume workouts further apart, by interspersing them with low-volume workouts of heavy loads.
#3. Reduced other stressors
To the extent that introducing variety with periodization involves focusing on developing one muscle group or strength quality at a time, then this would allow more capacity for recovery, by reducing the number of generalized stressors.
For example, some advanced bodybuilding programs periodize their focus on specific muscle groups. By increasing the training volume for one muscle group for a month while decreasing training volume for the other muscle groups (essentially putting them onto a maintenance-level program), the targeted muscle group can be developed very effectively, while keeping the overall generalized stressor level to a minimum.
Essentially, in this way, periodization “works” for preventing overtraining (the exhaustion phase) by reducing the total amount of muscle damage across the whole body that must be repaired at any one time, which focuses the adaptation energy on the desired adaptation.
What is the takeaway?
The general adaptation syndrome (GAS) refers to a generalized stress response that is observed in animals when they are exposed to a stressor. Animals have a finite amount of adaptation energy that they can devote to this generalized stress response, and exceeding this capacity leads to exhaustion.
Some strength training workouts and programs produce muscle damage, which seems to lead to a generalized stress response, and they can therefore be modeled by a GAS framework. However, other workouts do not cause muscle damage, and must therefore be excluded.
Periodization reduces the risk of reaching the exhaustion phase of the GAS framework (overtraining) by (1) limiting exposure to muscle-damaging workouts, (2) increasing the recovery time between muscle-damaging workouts, (3) or reducing the exposure to other stressors other than the targeted adaptation.