Adaptations to Training

Updated: Jul 30

Adaptations to Training

The general adaptation syndrome (GAS), developed by Hans Selye, describes how the body adapts to training. It provided a much-needed framework for the training process. When we undergo intense physical activity, our bodies will be subjected to stress. Stress is the body’s reaction to a challenge or demand. The body is always self-regulating its internal environment so it stays in a condition that is best to survive. This process is called homeostasis. When we do an intense training workout, our homeostasis is disrupted. This may include an increase in heart rate and body temperature and small muscle fiber tears. If homeostasis is disturbed, then the body will consider this as stress and start making adaptations. GAS theory helps explain how athletes and coaches can manage stress and fatigue to ensure the best adaptation from training. This was first studied on rats where they were exposed to stressful situations such as starvation, extreme temperatures, or very intense exercise.

When the body is subjected to stress, it enters the alarm phase where the individual's performance capability decreases. However, during the alarm phase, the body starts to adapt to the stress and gradually improves performance. This is the reason why so many people expose themselves to such intense workouts. They want to stress their body, so it enters into an alarm phase, allowing the body to adapt and improve.

Adaptations to Training

When stress is repeated with a well-planned training program, this process is repeated and performance keeps improving. One important thing to note is that the body’s adaptation can only happen during rest. Therefore, the body must be given time to recover after each workout.

Adaptations to Training

This theory provides the answer to why consistency is so important. To keep improving, our body needs to continuously be exposed to stress, and then rest so the body can adapt. This theory also introduces us to two important principles: specificity and progression. If the body keeps being exposed to the same intensity, the body does not need to adapt and improve and can cause stagnation and performance decline in an athlete’s level of adaptation. Therefore each session should be progressive, which provides larger stress on the body than the previous workout. If too much time passes after the first workout, performance will slowly start to deteriorate again. The training adaptation will be specific to the workout that it has been done. The GAS theory highlights how important it is to be consistent in our training and recovery. The GAS theory is also an important part of periodization, a plan developed by the coaches and athletes to reach the best possible performance for the most important competition that will be discussed in future blogs.

Adaptations to Training

Similarly training at an intensity that is too large or too frequent, which does not allow adequate recovery time, can lead to maladaptations by resulting in the alarm phase lasting longer, and the performance capacity decreasing further, thus reducing consistency. The GAS theory also states that if we train again before achieving full recovery, then our performance capacity will continue to decrease. This state is called over-reaching. However, if we give some time to fully recover, the improvement in performance capacity will be larger. This drastic improvement is called super-compensation

Adaptations to Training

Another alternative theory to GAS is the fitness-fatigue model. This model states that the training effect is based on two processes, the fatigue effect, and the fitness effect. These processes although they are distinct from each other, occur simultaneously during training. The first process occurs as fatigue accumulates, which reduces our performance capacity until we are fully recovered. The second process contrasts with the first as it shows that training improves our performance for that specific task (we become more efficient). However, after intense training sessions, performance decrements due to fatigue will be much bigger than our improvement in that skill. It is after we fully recover can we see our improvement in fitness, even though physical improvements have occurred during the workout.

Adaptations to Training

Even though GAS and the fitness-fatigue model are very similar to each other, there are some distinct differences which highlight how the body has different ways to improve performance. Unlike GAS, the fitness-fatigue model explains the improvements that occur due to adaptations in the central nervous system. As a skill is repeated, the body will be able to coordinate better and recruit more muscle fibers during a strenuous task (becoming more efficient). These adaptations occur quickly, especially for beginners. However, GAS better explains the physiological adaptations happening in the body such as the muscle fiber damage occurring after a workout which causes a decrease in performance. As the body recovers, it will adapt to withstand more stressful workouts by repairing these fibers and forming new and stronger fibers, increasing the ability to produce force. Whilst the improvements observed in GAS take a few days of recovery for the body structures to adapt, the improvements seen in the fitness-fatigue model are more immediate. It is important for a coach and an athlete to understand the different ways the body can adapt.

One of the major limitations of GAS and the fitness-fatigue model is that they both state that for training to be effective they have to cause fatigue. However, there are several training examples where even though fatigue is not present, there is still some improvement. For example, doing a short technical session does not create fatigue but it helps the body to improve performance. Similarly, an elite athlete may perform a light training session in which despite physiological changes (heart rate increases and sweating is released), it causes little fatigue post-workout. Examples can include tennis players practicing their serves, an Olympic lifter working on their technique with a training bar, or a marathon runner going for a slow-paced 5 K run. Fatigue is not always an essential part for adaptations to occur.

Thanks for reading, and as always stay fit!

Coach Darren


Bompa, T. O., & Buzzichelli, C. (2018). Periodization-: theory and methodology of training. Human kinetics.

Chiu, L. Z., & Barnes, J. L. (2003). The fitness-fatigue model revisited: Implications for planning short-and long-term training. Strength & Conditioning Journal, 25(6), 42-51.

Cleather, D. J. (2018). The little black book of training wisdom. Dan Cleather

Cunanan, A. J., DeWeese, B. H., Wagle, J. P., Carroll, K. M., Sausaman, R., Hornsby, W. G., ... & Stone, M. H. (2018). The general adaptation syndrome: a foundation for the concept of periodization. Sports Medicine, 48(4), 787-797.

Haff, G. G. (2004). Roundtable discussion: Periodization of training—Part 1. Strength & Conditioning Journal, 26(1), 50-69.

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