Psychological Stress Vs. Mechanical Stress: What's the Difference and Is it always bad?
I co-led a workshop this weekend on the science of stress, and my collaborator (yoga teacher/psychologist/generally awesome human) opened up with this question, which I think is apt; "What is stress?"
When most of us are asked to define stress, we can usually respond with the physiological manifestations of stress (digestion issues, shallow breathing, anxiety...) but we have a hard time giving a proper definition of just what exactly stress is. Here are a few examples:
"Stress is simply a reaction to a stimulus that disturbs our physical or mental equilibrium." - Psychology Today
"The non-specific response of the body to any demand for change" - Hans Selye (Who wrote amazing books about stress, including the excellent pun "Stress without Distress" as well as "The Stress of Life")
Now things get complicated because in science, mechanical stress has a completely different definition that has been around for hundreds of years:
"In continuum mechanics, stress is a physical quantity that express the internal forces that neighboring particles of a continuous material exert on each other while strain is the measure of the deformation of the material." -Wikipedia
So to put that in normal words, Stress is the load that's applied to a structure, and Strain is the resulting deformation from the load. Don't worry about it if that's a little opaque- I definitely needed to invest some time and research into understanding these concepts! To put this in context, take a look at a graph from Jules Mitchell's work on stretching- take a look at her in-depth explanation of stress and strain, and how it applies to muscles.
Knowing that stress is the load applied to a structure and strain is the deformation, you can see that the elastic region is the point where soft tissue fibers will bounce back to their original length and the plastic region refers to when the soft tissue fibers are permanently altered or negatively affected by the stress (i.e. injury!).
So back to stress: there's a psychological definition and a mechanical definition, but here's the bigger question...is stress bad? The answer is "it depends."
In terms of mental stressors, it depends on whether the stress is chronic or acute. Are you motivated by the stress of a deadline? Or are you dealing with the chronic stress of dealing with a long term health issue? Hans Selye, endocrinologist and stress researcher, coined the term "eustress" to refer to beneficial stress, and used the word "distress" to refer to negative stress. We've all experienced both aspects of stress in areas of our life, as well as acute (short term stress) and chronic (perpetual).
Back to mechanical stressors (physics/science stuff)- stress is not necessarily bad, depending on the amplitude of force and what the material can handle. If you go back to Jules Mitchell's work, she's looking at the maximum amount of stress muscle/ligament/tendon fibers can handle via "stretching" before breakdown. Some stretch is good- too much is destructive to the tissues. Conversely, the body needs mechanical input (i.e. mechanical stress) to make change- running is a mechanical stress, lifting, walking, sitting...those are all mechanical stressors that affectmechanotransduction, or how our cells metabolize the movement input we give it.
This may be you on stress, or how you feel trying to read this blog on mechanical stress.
"The stress applied to a material is the force per unit area applied to the material. The maximum stress a material can stand before it breaks is called the breaking stress or ultimate tensile stress. Tensile means the material is under tension. The forces acting on it are trying to stretch the material." -PhysicsNet.co.uk
I'll talk a bit more about the other aspects of psychological stress next time, but for now, just know that not all stress is bad and that there's a whole other world of stress in the world of physics and load science.