CHAPTER 4 – Stress and why it’s not so bad

“Everybody knows what stress is, but no one really knows.” Hans Selye [105]

Hans Selye is considered the father of modern stress research.  He was one of the first scientists to conceptualise and measure this ethereal force.  As with some of the most important discoveries in the history of science, Selye came upon the discovery of what he termed the “alarm reaction” incidentally when he was injecting rats with impure ovarian extract, and noted that they became sick.  He looked further at the physical changes in the rats and noted an unusual cluster of changes to their adrenal glands, thymus, spleen and gut [106]. He was able to reproduce the same responses by exposing the rats to cold temperatures, surgical injury, spinal shock, excessive muscular exercise, or intoxications with sublethal doses of drugs such as adrenaline, morphine or formaldehyde [107].  After years of research, he confirmed that ongoing exposure to the same physical conditions or drugs would follow the same three-stage process of initial physical changes, recovery and adaptation, then eventually exhaustion (and death).  He called this model the “General Adaptation Syndrome.” [107]

The General Adaptation model was groundbreaking, and the sheer volume of work done by Selye brought his theories to the forefront of the scientific community.  With time, the theory slowly descended from its place of adulation as other evidence came to light [108], but it has remained foundational, and Selye is still revered as the father of modern stress research.

Selye was never more profound when he said that, “Everybody knows what stress is, but no one really knows.” [105] The actual word “stress” is a western buzzword that has spread to multiple nationalities and languages.  It’s a concept that’s quite seductive.  As Richard Shweder poignantly noted in the New York Times, “Imprecise and evasive language may be a disaster for science but it is a boon in everyday life. ‘I am stressed out’ is non-accusatory, apolitical and detached. It is a good way to keep the peace and, at the same time, a low-cost way to complain.” [109]

The term stress “generally refers to experiences that cause feelings of anxiety and frustration because they push us beyond our ability to successfully cope.” [110] Scientifically, stress has been difficult to define.  Different researchers often use different definitions of stress depending on what they’re studying or what field of psychology or science they belong to [111].

In coming chapters I’ll come back to the modern adaptation of Selye’s model of stress, termed “allostatic overload”.  But first, I want to look at the basic concepts of stress and its functions in nature.

A broad concept of stress

To gain a better understanding of stress, it’s useful to step away from the medical concept of stress, and think about what the term means in other fields.

When an engineer thinks about stress, it’s usually in relation to a physical force on a material object.  As I said before, my son is a Mythbusters fan.  He was watching an episode the other day where the Mythbusters were testing the myth of Pykrete, a material that was nothing but wood shavings and ice.  They were testing to see whether it was more durable than ice alone, whether it was bulletproof, and whether it could be used to build a boat! [112] In order to test out these crazy claims, they made some in their workshop and compared it with normal ice.  How did they test it?  By stressing it - placing weights on the end of the block of the ice/pykrete until it broke.  (In the end, pykrete was ten times stronger than ice, was bulletproof, and they made a fully operational motor-boat from it!)

So the mechanical definition of stress is, “pressure or tension exerted on a material object.” [3] There are a few illustrations of mechanical stress, in our bodies and in everyday life, that are good metaphors for stress in our lives.

The Classical Stress/Productivity Curve

I confess I am NOT a musician.  I’ve never learnt to read music or play an instrument.  But I do know that when you first put a new string on the guitar, it’s unstretched – there is literally no force on it at all.  If all you did was tied the two ends of the string to the tone peg and the tuning peg, the string would remain limp and lifeless.  It wouldn’t be able to do anything useful.  It certainly wouldn’t play a note.

When the tuning peg is twisted a few times, there is some tightness in the wire.  The string is now under tension (i.e. stress).  It is now able to play a note of some form, so it can do some work and fulfill some of the function of a guitar string.  But the pitch isn’t good enough - the note is out of tune.

With a small adjustment, the string reaches its optimal tension and can play the correct note!  This is the point where the string is fulfilling its designed purpose.  Optimal stress equals optimal function.

With further tightening of the string, the perfect pitch is lost, but the string can still produce a sound of some form.  With more tension, the string can still make a noise, but it sounds awful, and the fibres inside the cord are starting to tear.  If the string were wound further and further, it would eventually break.

If this ratio of the tension of the string versus the usefulness of the string were to be plotted as a graph, it would look like an upside down “U”.  This is the classic stress/productivity curve.

The Exponential Stress/Productivity Curve

The second metaphor that I think illustrates a different concept of the stress/productivity relationship is a car.

As well not being a musician, I am also NOT a mechanic!  I know the important things like where the petrol goes, and how to drive them, but otherwise cars are very mysterious and powerful devices, their mystery is only exceeded by their power.

What I do know is that the engine is very much like the guitar string.  As more petrol is fed into the engine, the engine gets more powerful.  Soon, the engine finds its “power band”, a zone of maximum torque that can be achieved at moderate revolutions.  As the engine is given more gas, the power output declines from the middle of the power band.  If the engine was maxed out then the amount of functional power coming out is reduced.

This would plot as a similar graph to the U-curve of the stress/productivity curve.  But cars not only have engines, but also a gearbox.  The gears allow for multiplication of the work done (the productivity) for the same stress on the engine.


As a child, I didn’t dream of becoming an astronaut, but I was interested in space.  The beauty of our night sky is as stunning as any forest, river or mountain.  I would read of the astronauts in rockets and in space stations, floating around in zero gravity, swimming through the “air”.  That sounded like a lot of fun.

But zero gravity isn’t particularly good for you.  Some early astronauts had to be carried off their landing craft on stretchers because the effect of zero gravity would render these men weak and atrophied.  They boarded the spacecraft at the peak of their physical strength and fitness, but after only a few weeks without gravity, their bodies resembled that of the elderly (although without the wrinkles) [113].

It’s a general principle of the human body that any tissue that isn’t needed shrinks in size - a process called atrophy.  In zero gravity, the body doesn’t need as much muscle, so the muscles shrink.  The body doesn’t need as much bone strength, so the bones weaken.  There is no gravity to pull their blood away from their head, so the blood volume decreases.  Because there is less muscle to pump blood to, and less blood to pump, the heart doesn’t work as hard, so the heart muscle atrophies.  The net effect of zero gravity is to make you physically weak [113].

On the other hand, too much gravity is not great either.  Animals can adapt to small amounts of hypergravity [114].  But large amounts aren’t so good.  During astronaut training, NASA subjects the rookie spacemen to rigorous tests including placing them in a large centrifuge and spinning it very fast.  The result is an increase in the gravitational forces applied to their bodies.  The increased gravity makes everything in the body heavier and their blood is pulled towards the legs and away from the brain, which leads to what is known as G-LOC (Gravity-induced Loss Of Consciousness).  In other words, the heart can’t fight the increased force of gravity and the brain loses its blood supply, which makes you pass out.  Josh McHugh did an entertaining piece on his experience with G-LOC and the centrifuge in Wired (2003) [115].

In this sense, gravity is to us physically like stress is to us mentally.  Without gravity, our physical bodies turn to mush as we slowly weaken from the inside.  Too much gravity, and our physical bodies are slowly squashed by the invisible weight of the extra G’s.  Our bodies work best at 1G.

Mechanical stress and you

How does all this fit with stress?  One of the reasons why gravity gives you strong muscles and bones, and zero gravity gives you weak muscles and bones, is because of resistance.

Movement involves work.  We do "work" everyday in simple everyday activities, because our muscles and bones have to apply a certain amount of force in order to overcome gravity.  Our muscles adapt by growing the muscle fibres to provide that force, and bones remodel themselves to provide the maximum resistance to the loads that gravity and the muscles put through them.  We’re not aware of this day-to-day because we never experience prolonged changes in our gravitational fields.

But when we need to do more work than our muscles are accustomed to, our muscle fibres increase in strength, first as the nerve networks that supply the muscles become more efficient, after about two weeks of ongoing training, the fibres themselves increase in size [116, 117].  The growth in muscle fibres is caused by three related factors: mechanical tension, muscle damage and metabolic stress [117].  Mechanical tension involves “force generation and stretch”.  In other words, the muscle fibres are stretched just beyond their usual capacity, and they actively fight against the resistance.  This damages the weaker muscle fibres, which are repaired.  The remaining muscle fibres are forced to adapt by growing larger because of the stimulation of growth factors [117].

One of my favorite "Demotivator" posters says, "That which does not kill me postpones the inevitable" [118].  Of course, the phrase that they’ve parodied is, "That which does not kill us makes us stronger."  Why is there truth to that idiom?  Adversity occurs when life circumstances come against us.  In other words, adversity resists us.  In the arm wrestle between adversity and overcoming, work is involved.  We have to fight back.

In a similar way, we grow when adversity pushes us just beyond what we have done before, stretching us.  We may sustain some damage in the process, but that helps to reduce our weaknesses, and forces us into growth as we heal.  When we push back against adversity, the “cells” of our character grow.

Of course, we all know examples where muscles fail under intense or prolonged loads.  I vividly remember the pictures of the UK’s Paula Radcliffe, succumbing to the grueling hills and scorching Athens heat with only four miles left in the 2004 Olympic Marathon.  Muscle failure from excessive stretch or excessive endurance parallels the allostatic load response, which is what people commonly referred to as ‘stress’.

Scientific evidence that stress is positive

There have been recent studies in animals that demonstrate that stress is physically as well as mentally enhancing.

Neurogenesis is the process of new nerve cell formation.  Studies of rodents placed under intermittent predictable stressors showed an increase in neurogenesis within the hippocampus, which is the part of the brain related to learning and memory.  Along with this enhancement of neurogenesis, the function of the hippocampus increased, specifically hippocampal-dependent memory, with a reduction in depression and anxiety-like behaviours.

As Petrik et al noted in their review, “Contrary to stress always being ‘bad’, it has long been appreciated that stress has an important biological role, and recent research supports that some amount of stress at the right time is actually useful for learning and memory.” [119]

Lessons from stress

So what can we learn from stress?  How do we use the stress that we are exposed to every day to make us grow strong and durable?

Firstly, like the guitar string, we need to learn when we are in tune, at the peak of our productivity.  Or like the car engine, what it feels like to be in the power band.  When we know where our sweet spot is, we can operate within it, achieving our best in life without doing ourselves harm.  This is the first point that we need to identify on our own personal stress/productivity curve.  This is the point of maximum productivity.

The other life principle to be gained from the car engine analogy is that not all of us are high performance engines.  I would love to think that I’m a F1 racing engine - highly tuned, supreme power - but I recognise my limitations.  I would even settle for a 5-litre V8, but I know that I’m probably more like a well-tuned V6.  We are what we are.  Sometimes we apply the most stress to ourselves when we try to drive in the power band of someone else’s engine.  We need to accept who we are.

It seems logical that if too much stress is bad for us, then having little or no stress is good for us.  But like the new guitar string, minimal stress makes us unproductive.  Like zero gravity on the body, little or no stress makes us weak.

And we need to understand that a bit more stress is ok.  It’s inevitable that we are going to be stressed beyond what we usually cope with at times.  But without that challenge, there would be no growth.  Challenges usually hurt.  You can’t have growth without pain.  In the muscle analogy, at the stretch at which peak growth occurs, muscle fibres tear and the lactic acid build up in the remaining cells can be very uncomfortable.  The key is learning how far we can push ourselves before we start to falter and fail.  This is the second point we need to discover on our personal stress/productivity curve.  This is the point of maximum growth.

Once we understand our own individual points of maximum productivity and growth, we can use them as guides to our personal growth and achievement.  Actually, I should specify that these are our starting points, since as we face challenges and experience growth, the points will change slightly.  We can remap those points and continue in our pattern of growth and development.

Pushing ourselves into just enough stress to achieve growth, then pulling back to rest and restore, is a pattern of growth that is seen in many facets of the natural world and the human body.  Body builders and athletes use this method all the time in their training.  They push themselves with more repetitions and heavier weights, or longer or faster runs, then they pull back to consolidate their gains.  During our adolescence, our bodies naturally go through growth spurts - periods of rapid growth followed by a plateau, before the next burst of growth hormone hits us again.  Even tree rings demonstrate that growth and consolidation occur all the way through the natural world.

This is the Stressed-Rest cycle.  The studies in animals on neurogenesis strengthen the theory, because it was the animals that experienced bursts of stress that showed enhanced neurogenesis, memory and reduced depression/anxiety behaviours.

If you want maximum personal growth, constant stress does not help.  There has to be times of rest.  Some people think that rest time is wasted time, reducing productivity.  But as explained, without rest time, productivity rapidly falls away.  Without rest, stress goes bad, leading to allostatic overload.

So in summary, excessive stress is bad.  But if all stress were bad, then we would all crumple any time that something became difficult.  So stress is not a force for evil. Stress is part of our normal everyday lives, and is vital if we are to see ongoing personal growth.

We know from living life that we all don't fall in a heap when things go wrong.  We have in-built ways of coping that help us to absorb troubles and adversities and like emotional photosynthesis - turn them into fuel for growth.

This is the science of resilience, the counterbalance to the forces of stress that help us cope and adapt in a rapidly changing natural and social environment, the Yang to allostatic overload’s Yin.  A discussion on the science of stress is not complete without a discussion of resilience, which I’ll discuss now.