Stress and Adaptation

Stress seems to be a bad word in our society. We often think of it as something we should avoid or minimise. However, for physiological change – or adaptation – stress is a necessity. This post explores how and why stress causes adaptation, in other words, why training can make us better athletes.


I have tried to keep this post relatively brief, but for those who want the quick summary…

  • Exposure to stress is essential for adaptation.
  • Training must challenge the body to be considered a stress.
  • Following a stress, performance is initially decreased.
  • Increased performance occurs later, after recovery.
  • Adaptations are specific to the stress encountered.

What is Stress?

A stress can be considered as exposure to a stimulus that causes our body to move away from the norm. It challenges our bodies ability to maintain homeostasis, i.e. our tendency to keep our internal environment constant.

Consider lifting a near maximal weight, like me below…

Squatting at the 2014 Oceania Championships

While trying to overcome the weight of the bar, my brain is fighting to activate as much musculature as possible, resulting in my muscles attempting to contract with maximal force. These systems are under huge stress, as they work as hard as they possibly can, to move the bar against the force of gravity.

However, if the weight were lighter then the stress would be far lower, or even removed. The brain would have no trouble sending a signal to activate enough musculature, and the muscle easily able to generate enough force to overcome the resistance. It would not be challenging, and thus it would not be considered a stress.


Our bodies don’t particularly like stress. They like to maintain homeostasis, and prefer things to be kept under control. So, once we have been exposed to a stress, the body will attempt to find ways to minimise the effects of a similar stress in future. This is adaptation.

In the example above of lifting a heavy weight, we specifically mentioned that both the nervous system and muscles were stressed. When adaptation occurs it is specific, so the adaptations from the above example will occur directly to these areas.

The nervous system will adapt so that it is able to recruit more of the available muscle, perhaps in a more coordinated manner. While the muscle may hypertrophy (grow), so that there are more muscle fibres available to contract and produce force with. The combination of these factors will result in an enhanced ability to produce force.

These adaptations mean that the next time the body encounters a heavy load, it is better able to handle it – the stress has been lowered.

The Fitness-Fatigue Model

The Fitness-Fatigue model gives us a visual representation of the phenomena described above. In the figure below, the red line indicates an athletes level of performance, while the dotted green line indicates a “fatigue” after effect, and the dotted blue line a “fitness” after effect. Called after effects because they are occurring after the training stress has occurred. In the figure below, training has occurred at the same point as the vertical axis.

Fitness fatigue.png
The Fitness-Fatigue model

When you train, if that training is challenging enough, you stress the body in such a manner that performance initially decreases. If it were a bout of strength training, perhaps there is damage to your muscle fibres, causing them to have reduced force producing capabilities – making you weaker. This is the fatigue after effect, it has a substantial negative effect, but it disappears quickly.

After this initial reduction in performance, the red line begins to rise – to an even greater level than it was initially (super compensation). Continuing with the strength training example, this may be muscular hypertrophy which increases the bodies force producing capability by adding more contractile units – thus making you stronger. This is the fitness after effect, it has a gradually rising positive effect, that resides for longer.

The summation of the fitness and fatigue after effects produce changes in performance. Soon after training the fatigue after effects dominate, and the fitness after effects are only slowly rising, resulting in decreased performance. Then, once fatigue has begun to dissipate, and fitness is still on the rise, performance begins to rise. Eventually, in the absence of another training stimulus, both after effects subside and performance drops to its initial level.

It should be noted that the after effects within this model are specific. If you trained your upper body, then the effects will be primarily on the upper body. So while the upper body may be fatigued the next day, your lower body is essentially good to go. Sure there may be some systemic effects, but the majority of the fatigue will be within the upper body.

Final Thoughts

Although challenging at the time, stress is essential for our ability to adapt. Stress may cause temporary decrements in performance, but given sufficient recovery, adaptations will occur resulting in enhanced performance.

My next few blog posts will continue to cover concepts that expand upon this information. Specifically, these will relate to training principles, over/under-training, and long-term training organisation.

If you have any questions then ask below, or feel free to comment on my Facebook or Instagram. Catch you next time!

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