The Injury of Pilot Fatigue: Is Fatigue a Stress or a Strain ?


Fatigue: Is It a Stress or a Strain, that is, an injury? Is fatigue an injury to the human body from which we need time to recover? Or is fatigue just being tired or over tired, a stress for which a good night’s sleep is the common remedy?

That is the question: is fatigue just a stress on the body and mind and as such something from which the body and mind can bounce back without any damage? Or is fatigue rather something more insidious and injurious than just a stress? Is it possible that fatigue is actually a strain, that is to say,  an injury, damage to the body and mind? If fatigue is an injury to the body and mind, an overstress resulting in a strain, does the body and mind need time to heal back to health from this injury? Is the time of a “good night’s sleep enough time to heal from this injury?

Does repeated stress lead to more damaging strain? Can the road to recovery from the strain of fatigue to the body and mind be a lot longer than just one good night’s sleep? Is the body and mind being damaged beyond the ability to recover in a day or a weeken

Human beings who has spent many nights and days working multiple shift hours far in excess of any reasonable eight or ten hour schedule can be over tired, falling asleep at the switch as the saying goes from fatigue. Yet they are there trying to do a good job, a necessary job and trying to have a life outside of work at the same time. The one thing that has not been discussed is does recovery from fatigue take much more time than just one good night’s sleep. If so, why? Is a person somehow injured in my mind and body to the extent that they need to heal? If so, where was the injury, how can a person feel it and how can they measure it? How much time is needed for full physiological recovery of body and mind? Is sacrificing the health of body and mind for a job well understood? If so, are people being separately compensated for both the work done and the sacrificing of the health of body and mind?

There are two issues to working at night and working extended hours repeatedly, the issue of compensation for the work and compensation for the hours past any reasonable shift.

But there are often more questions about fatigue than answers.  What is the pineal gland anyway and how does it work? Does the brain need oxygen and sugar to function? Why does worry have the same affect as caffeine? Why is a hot shower so refreshing when tired? Why do kids fall asleep when tired wherever they sit down? Why do older folks struggle often with sleep?  Why do flight crew often feel so tired on weekends that they just want to relax and do nothing stressful, just recover and hope for restful sleep? How and why does fatigue knock your brain out like a light switch turning off, even when you are not lying down in bed? How does it know to do that? What else do we not know about fatigue?

So, in my curiosity I harkened back to my university days studying metallurgy. We studied the physical relationship between stress and strain on a metal sample and on samples of wood, plastic, ceramics and other material. Stress is the force that is applied to the metal sample and strain is the amount of deformation that occurred to the sample piece as a result of the stress.

As students we found was that for the most part, metals deform elastically under lower levels of stress and essentially return to their original shape, size and strength. This means that the stress is bourne by the material and it springs back into its original being.

In physiology terms, we might say that one all-nighter isn’t so bad; just get a good night’s sleep and you will bounce back, good as new and be ready to go just fine. Probably all true, especially so for lab studies of human being subjects.

Now back to the metal samples. As we continued to add stress to the metal samples, somewhere down the line we got strain that is no longer elastic. The sample no longer bounces back. The sample now begins to deform. It is still strong and has some of its original strength, but it has become bent, stretched and weakened.  The stress that was put on the sample past the elastic strain point damaged the sample. It is deformed plasticaly, that is, it will no longer spring back into it’s original size, shape and strength. It is deformed into a new shape. It is still one piece, but deformed. It will not now nor ever go back into its original shape. Moreover, if the stress is continually applied, not only does the strain result in a deformation in size, shape and strength, the sample will eventually break, fail and just come apart, often with a very loud bang.

Now, back to the human physiology story. Again does the human body and mind react in a similar manner, that is to say, that the body and mind can take some stress, some sleeplessness, and bounce back elastically with just a good night’s sleep. But what happens to the human body and mind when the stress of sleeplessness is applied continuously and applied over the ability to take this stress undamaged?

Can the stress eventually cause a strain, that is, damage to the body and mind, damage that one good night’s sleep is insufficient in time and regenerative power to cause or allow a recovery? Can we over stress the body and mind with fatigue? Can fatigue be damage that affects the body and mind such that it is injured and needs time to recover from the injury? Is fatigue more than a stress? Can fatigue cause a strain or injury?

The answers to all of these questions is neither clear nor well known. But these questions need to be asked. Is fatigue more of a strain at some point than just a stress? Can we do injury to our bodies and minds by stressing them with fatigue to the point that they are damaged in some manner and no longer function well? Can this damage be such that one good night’s sleep is insufficient time in which to recover? Have we broken something that needs mending? Have we injured something in ourselves which needs recovery?

Is fatigue more of a strain than a stress?


Published by Capt. Paul Miller

Aviation safety expert with 43 years in the sky

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