Stress and Endurance sports and cycling_cover

Stress and YOU

The absence of stress is death

-Hans Selye

Stress and Endurance Sports

It has always been there until somebody gave it a name. Stress affects absolutely every single aspect of life, yet most of the lay press, radio, television and now the internet constantly discuss it, though without real awareness of exactly how far reaching the concept is and that it does represent not just an emotional problem, caused by deadlines, debts and/or annoying coworkers.  In an athletic paradigm stress takes the form of overtraining and has ended many a career of all levels – from rising stars to great champions.

Why Does Stress Exist?

Long ago, in the second half of the nineteenth century Claude Bernard made an observation that the internal medium of any organism is not just there to carry nutrients around, but that it is the fixity or constantly balanced state of that millieu interieur that is required for free and independent life. Today we call that homeostasis. Everything inisde the skin and even the skin itself constitutes that internal medium; if anything is allowed to deviate from that norm, the body will respond – with both short and long-term effects.

The more extreme examples are the so-called fight-or-flight. A bear jumps out in front of you, you suddenly go into hyperdrive and sprint harnessing all resources and once (hopefully) out of harm’s way, life gets back to normal, though not before a brief stage of exhaustion.

Homeostasis is paramount for survival, while at the same time, possible ‘stressors’ come in many shapes, forms and sizes. Therefore the most robust way of dealing with all those ‘disturbances’  from an evolutionary point of view is by a an all encompassing general response – think of flooding a burning field rather than spraying it with sprinklers.

General Adaptation Syndrome

As a young medical student Hans Selye  observed that no matter the disease/problem – whether it was severe loss of blood, infection or advanced cancer – ALL patients exhibited loss of appetite, muscle strength and lack of general motivation to do anything. You could see on their faces that they were being sick. What was it that was causing the same symptoms in quite different diseases?

Many scientists and physicians before him, discovered bleeding stomach ulcers and enlarged adrenal glands above the kidney of burn patients, in animals suffering acute infections, etc, though as it is sometimes quite easy to do in science – it was a case of seeing the trees and not the forest…

It wasn’t until 1936 that Hans Selye experiments on rats presented an answer. No matter the treatment – exposure to cold, spinal injury, excessive physical exercise (my emphasis), or non-lethal doses of various drugs all caused the same syndromes that followed identical three stages (alarm, resistance, exhaustion). And so the concept of general adaption syndrome or what we call stress today was born.

Stress and Endurance sports General_Adaptation_Syndrome

General Adaptation Syndrome (Wikimedia Commons)

Stage 1: Alarm

After the initial injury or exposure to a stressor, in 6-48h the liver, thymus and lymph nodes decrease in size. Muscle tone diminishes, muscle tissue starts to get broken down, body temperature drops. Erosion of the stomach lining happens (my emphasis). How many athletes/people do you know that have “gut issues?”  Furthermore, fat tissue starts to disappear. The adrenal glands, located on top of the kidneys, release their cortisol containing granules into the bloodstream (more on that further below). At this point the resistance or the ability to handle the stressor is diminished – if the offender is strong enough, even death might result. In simple terms, the best time to get sick. This stage is REVERSIBLE – ie if whatever alarmed you disappears, your body goes back to normal. If you outrun the bear, just met that deadline, exit that job interview etc. a warming sense of relieved exhaustion comes over you.

Stage 2: Resistance

If the stressor is still around your body adopts a head in the sand approach and doesn’t get bothered much by it and even so more or less goes back to it’s normal functions – you gain the lost weight back, etc. However, the adrenals are not easily fooled and if the stressor is still around (even up to 3months), the glands get notably enlarged in order to secrete even more cortisol. The release of growth and gonadotropic (and as a result sex hormones such as testosterone) (my emphasis) is stopped while the production of hormones, responsible for the speeding up of metabolism is ramped up.

Doping side note #1: Human growth hormone (hGH) and testosterone are among the most widely abused performance enhancers in all sports. The important takeaway point is that in the resistance stage you are in a way anti-doping yourself. I am too lazy to look at athletes (I am sure there are many) who were diagnosed with low testosterone levels and subsequently got a ‘therapeutic use exemption’ aka green light to dope, though some notable figures that suffered from diminished testoterone levels and were even forced to retire due to the condition were Mr. Prologue Chris Boardman and 2:04 marathoner Ryan Hall. Overtraining is just another word for chronic stress (more details on why in the following paragraphs).

While everyhing might seem fine, there are inevitable consequences – the stressor is still around even though you might not realise it until….

Stage 3: Exhaustion

‘Cause nothing lasts forever, even cold November rain

-Guns’N Roses

In the words of the Guns’n roses, nothing lasts forever and if whatever is cauisng the stress continues, the same symptoms as during the alarm reaction reapper – now you can’t handle even a little of the thing that alarmed you in the first place. This stage IS NOT REVERSIBLE. In extreme cases and in some animals it may even result in death.

Before continuing, the most important takeaway points are:

No matter the cause – any deviation from homeostasis causes the same cascade of events.

If whatever caused the sway from normal does not disappear, after time the body WILL ALWAYS enter an irreversible state of exhaustion.

While the above is pretty clinical what does it all have to do with life and endurance sports?

Let me explain…

As pointed by Prof. Selye himself, only the dead have no stress;  things are out to get us, more metaphorically these days (bills, debts, managers, air pollution, etc.) than literally (bears, tigers), and logically if they all cause the same general response – the effect of many stressors is cumulative – they all add up and adaptation energy is finite. Are we all doomed?

Not exactly.

As you can imagine a skin burn, an insect bite, loud noise, or swimming in freezing water are not the same thing as far as our bodies are concerned. While sharing the same general response, stressors possess as well a specific effect that acts on certain body organs/systems with an additional distinct reaction.  Therefore different people respond differently to the same drug, and why some people don’t get sick when flu season comes around. If all the body systems are like chains – it is the weakest link that breaks.

In addition we develop conditioning, ie the horizontal line in the graph above gets higher for some stressors. Physical exercise (cycling, running, etc) is a stressor and getting fitter is a way of becoming conditioned towards it. Babies cry all the time because everything and I mean everything around them is new and alarming. Last time you went to a new place, unless that place was an active war zone, you didn’t give a single thought about freaking out, let alone cry.

Ineffective coping strategies cause distress – a significant stress response

This is where it gets tricky and a lot of people in modern fast paced societies, wear stress as a badge of honor, a sign they are trying hard, etc. and brush off any warning seems, bar the very obvious ones with the words:

“But I Feel Fine!!!”

Why is carrying that high strung badge of honor a bad thing?

While in the stage of resistance, indeed most systems and organs go back to functioning as normal. Even the higher tolerance towards whatever was causing the stress, feels like second wind. When we talk about sports, you might have an amazing race ‘out of nowhere’ (I am talking shattering previous personal bests by 5-10+%), so it might lead you to think that you are bouncing back from all the accumulated fatigue. HOWEVER, as mentioned earlier the adrenal glands are not just pouring cortisol into the bloodstream, they have become larger so they are literally flooding everything.

What does that mean?

The HPA Axis

We have a brain for a reason and it runs the whole show. In the case of stress when whatever that exceeds your coping abilities immediately sets up a chain reaction. (As a note – this is a general overview and not a biochemistry lesson). The events that follow try to accomplish biological and physiological adaptation.

Through many inputs the hypothalamus receives a signal (limbic system ie emotions, or from the organs, skin, etc.). When that gets interpreted as a stressor it releases Corticotropin releasing hormone (CRH) that reaches the anterior pituitary which in term releases adrenocorticotropic hormone (ACTH) that acts on the adrenal glands (cortex) who release cortisol and epinephrine (adrenalin) into the bloodstream. The presence of cortisol tells the hypothalamus and the anterior pituitary to produce less of CRH and ACTH in a negative feedback loop (red lines).

stress and Endurace sports HPA_Axis_Diagram_(Brian_M_Sweis_2012)

The HPA Axis (Wikimedia Commons)

Doping side note #2: Low cortisol levels might indicate that external sources of cortisONE (that has the same effects as cortisOL) had been used and as a consequence have over-suppresed the natural levels below normal through the mechanism described above. Sadly this is a constantly occurring thing in cycling (low cortisol levels) and teams plead innocence, rather than sidelining athletes.  Why would anyone want to do more or less ‘put stress in their bodies’ is covered in the following paragraphs.

The whole complex consisting of the hypothalamus, the anterior pituitary and adrenal glands is referred to as the HPA axis. Though this is semantics, the important question is:

What do cortisol and adrenaline do in the body (and why chronic elevation is a bad thing)?


A quick reminder that stress aka the attempt to return to normal/fight-or-flight is paramount for survival. In order to return to normal, it takes energy or in biological currency usually glucose.

So on to cortisol and adrenaline…

First and foremost cortisol is a glucocorticoid aka glucose metabolism influencing. It counteracts insulin and causes a spike in blood sugar. It stimulates the making of new glucose (gluconeogenesis) so there is a ready supply of it. If you have a tendency for Type 2 diabetes this is a good way to go over the line. In addition cortisol causes a ramp up of fat metabolism by depleting precious energy stores (this is not as good as you might think) and the breakdown of muscle and lymphoid tissue in order to obtain proteins – you lose weight. All of the above happens in order to have all available energy sources at maximum, so you are sure to give it all when running away from that bear and have the energy available to recover afterwards (so you can sprint away from the bear another day). The bad news is that losing muscle mass is never a good thing and chronic stress/cortisol elevation causes you to crave sweet sugary foods in order to replenish the glucose you are constantly burning (remember glucorticoids) in order to ‘cope’ with the stress. Burning glucose rather than fat is not something you want to be doing in the long term.

Furthermore cortisol causes a suppression of the immune system, do it long enough and even simple colds make you bedridden and when flu season rolls around you are sick ALL the time. Ever wondered why top athletes who should be the epitome of health get constantly sidelined with colds and stomach bugs when racing season picks up? Here’s your answer.

As well cortisol/glucorticoids are powerful anti-inflammatories (think mega turbo ibuprofen). In the case of not rejecting a transplant/skin graft/etc this is a good thing. In the case of normal (athletic) life working out causes muscle breakdown, damage and overall inflammation/soreness. Getting rid of it quickly might allow you to race/train and patch up that semi broken knee when you really should be resting, therefore you can see the potential of abuse where performance and money are on the line.

As with all quick fixes the final price is high…

Cortisol suppresses bone and collagen formation – long term effects: osteoporosis (brittle bones) and ligament/tendon/connective tissue and fascia problems. It puts a whole new meaning into stress fractures and chronic ankle sprains doesn’t it….

The levels cortisol naturally goes up and down throughout the day more or less together with the 24h light/dark cycles- it is what makes you relaxed before going to sleep and what naturally wakes you up. If you have to get up couple of times in the wee hours of the night and can’t fall asleep – you have abnormally elevated cortisol – you are stressed! Also this is the main cause of “jetlag.”

Last but not least, cortisol increases metabolism/turnover of all the stuff that transmit signals in your brain – you feel tired, depressed, and can’t sleep.

Though no enemy works alone…


The same factors that cause the release of cortisol make adrenaline to be released as well. Adrenaline truly is the fight-or-flight hormone. It also causes the rapid breakdown of muscle and liver glycogen so that glucose gets in the bloodstream. It ramps up heart rate and increases blood pressure and breathing – you are ready to go for it or sprint for it.

And it all happens because we have a brain…

Chronic stress causes an overactive sympathetic nervous system (fight or flight) and a PARAsympathetic nervous system (homeostasis) that can’t cope. Therefore one of the methods to see how stressed you really are is Heart Rate Variability – the difference between each heartbeat, strabgely the more consistent (less variability) the more stressed you are. There are apps to do that, though you can see if your heart rate raises as you inhale and drops as you exhale.

Stress and endurance sports HRV heart rate variability

Heart Rate Variability

That brings me to the next and possible most important point of this article

Stressors, Overtraining and YOU

Всички болести са от ядове, а всички ядове от гадове.

-Bulgarian proverb

Loosely translated the above proverb says that all disease are caused by stress and all stress is caused by arseholes (excuse my French).

I am repeating myself that athletes or not we are humans first and as such whatever happens in “normal life” will definitely be reflected when out in fields running, cycling , swimming, etc. Therefore reducing and realising how detrimental stress can be, is probably one of the most aspects of living a healthy life and high athletic performance.

I am sure by now you have gleaned that overtraining is just stress with an athletic flavor and it follows the same three stages. Particularly the second resistance stage is tricky – when already on edge during raceday and you have an amazing out of the water performance, it is always a red flag (especially since in endurance sports improvement is gradual). You don’t need 20+h training weeks to overtrain, you just need sufficient amounts of stress. All those great stars on magaine covers from 10, 15, 20 years ago that you never heard again? That rising star that “made it to the big league” to only crash and burn? Athletes with low testosterone? Stressors in all their shapes and forms (that includes travel, to much training, etc) were among the top 2 reasons.

Rarely something in biology is black and white – it doesn’t just happen. Crashes and sudden physcial trauma aside, when you finally break down it didn’t just appear out of the blue. It has been going for quite a while under the surface.

What exactly has been going on?


Pretty much everything can be a stressor, it is how you react to it that makes all the difference in short how you deal with it, though for convenience, it is best to separate them into three general categories, which are not exclusive and there might be some overlap.

Physical: This is the stress that influence directly the physical body – bones, muscles, etc. Training is a stress and SLIGHT muscle stress is what makes the whole thing beneficial, hence the increased importance of recovery. Muscle imbalances can be the outward expression of that. Some examples

  • Poor fitting shoes/bike
  • Prolonged sitting
  • Endurance training
  • (High-intensity) Training
  • etc.

Biochemical: The human body runs because of tightly regulated biochemical cascades. Any disturbance there would cause the internal balance to deviate from homeostasis.

  • Caffeine
  • (Second hand) smoking
  • (Prescription) drugs/doping
  • Air pollution
  • “Starving yourself”/low calories
  • Low fat diet
  • Junk food, sugar, etc.
  • Vitamin deficiencies

Mental and Emotional: this is the category which almost everybody is familiar with. It can influence sensations, learning and decision making.

  • Demanding/stressful job
  • Strong emotions: negative AND/OR positive
  • Noise
  • Deadlines
  • Relationship/family turmoil
  • Lack of sleep
  • Travelling (across timezones)
  • Traumatic personal/family events

The list can go on though here is where I hand it over to you:

Stress list

The idea for this goes to the great Dr. Phil Maffetone.

Nobody is immune to stress, as you saw from the above examples, it can all add up without you realizing it.

Therefore take out a sheet of paper, seprate it in three columns;

  1. Put physical, biochemical, emotional at the top
  2. Take a couple of days, even a week (yes seriously) to write down stressors in your life
  3. Cross out the ones that you have zero control over
  4. Prioritize the biggest one in each category; put them on top
  5. Circle one (yes really) and try to eliminate it
  6. Repeat

Seeing is believing and most of us do not realise how many things are out there that wreak havoc on daily life and ultimately performance. If you have big stressors that you have no say over maybe it is time for some big life changes. Chronic stress is the single thing that can throw a monkey wrench in a seemingly perfectly running machine that is the human body.  My ancestors in the quote above, realised it long ago, now it is time for all of us to master the concept from them. As somebody said – learning to say “No” is probably among the most valuable life lessons.


The input might be different – sadness, poor fitting shoes, drugs, loud noises, cold weather, starvation and the list can go on and on. HOWEVER, the ouput and result is the same- General Adaptation Syndrome or Stress. I leave you with this memorable quote form teh father of the stress concept:

We must not suppress stress in all its forms, but diminish [negative] distress and facilitate [positive] eustress, the satisfactory feeling that comes from the accomplishment of tasks we consider worth while.

-Hans Selye

As such with a satisfactory feeling, I hope to have given you a pleasant read and I would like to hear you comments and opinions in the comments sections below.

Like TheTallCyclist on Facebook and Subscribe via RSS or Email for future updates.

For further information check the ever-increasing Reading List

I welcome comments, however, before asking a question please visit the Frequently Asked Question (FAQ) page.


The Stress of Life – Hans Selye

The Stress of Life

Why Zebras Don’t Get Ulcers – Robert Sapolsky

Why Zebras Don't Get Ulcers, Third Edition

This article is for my personal use and educational purposes only, please always consult a licensed health professional. I cannot be held responsible for any damages caused by the information contained in this article.

A drop of support means an ocean of gratitude.

If you find motivation and value in the content of TheTallCyclist, consider making a donation.


All images are copyrighted to their respective owners. I do not own any of them.


  • Bernard hinault Paris Nice
  • Wikimedia commons
  • Polar



Print Friendly, PDF & Email