Psychology has drawn a number of insights from the engineering field. So it strongly aroused my curiosity when a psychology student with an engineering background raised the question of whether the psychology field had considered differences between the terms “stress” and “strain”. She explained that whereas these terms might seem similar, they are explicitly differentiated in engineering. This question inspired me to further investigate engineering terminology and principles that relate to stress and strain. Here are some insights that might apply.
What is Stress?
Psychology originally borrowed the term “stress” from engineering, where it means the amount of external force applied to a specific area of material. Psychologically, an equivalent notion is a degree of external demand or challenge or threat we face. Not all stress is bad. Indeed, a moderate amount of stress can sometimes lead to benefits such as increased focus and motivation as well as improved cognitive functioning.
Beneficial stress is sometimes referred to as “eustress”, meaning that it is no more than moderate, is normal for the situation, and seems manageable. An example might be feeling some stress ahead of an exam or a sporting competition that we are nonetheless well prepared for. Eustress might be contrasted with distress, which implies a degree of suffering.
What is Strain?
In engineering, the term “strain” means that a material has been deformed, or altered in shape as a result of the stress upon it. Different materials have a different stress-strain curve. For example, a rubber band will quickly change shape even with minor stress, whilst bamboo will bend more than many other forms of wood or metal, which in turn might be subjected to considerable force before they start to bend.
In psychological terms, the equivalent notion to our stress-strain curve is our “stress signature“. It helps to recognize what kinds of symptoms or reactions we experience when facing mild, moderate or severe stress. More severe or prolonged stress will likely have a greater negative impact on our mental health and general functioning.
Elastic and Plastic Strain
Many materials that are strained will return to their original shape such as a rubber band no longer being stretched, when it is said to have been elastically deformed. However, beyond a certain “yield point” a material will not return to its original shape, such as a bent tent peg, and is said to be plastically deformed.
Psychologically, we might experience a certain amount of stress before it has a negative ongoing impact in terms of undue strain. Preferably we would generally contain our stress to a level or duration that might lead to some elastic strain as opposed to less reversible plastic strain. It helps to recognize when we are approaching our psychological yield point so to speak, beyond which level any ongoing stress could lead to less reversible strain, such as experiencing severe burnout from prolonged excessive work demands.
What is Strength?
Engineers generally define the strength of a material in terms of how much stress it can withstand. Yield strength is how much stress a material can be subjected to without becoming plastically, or irreversibly, strained. Ultimate tensile strength is how much a material can take without breaking. Repeated stress on a material can lead to fatigue. Fatigue strength is the stress a material can withstand any number of times without breaking.
In psychological terms, it’s important to recognize when we risk approaching a “breaking” point beyond which we might not be able to continue our usual activities or roles, such as through severe burnout or clinical depression. We might also appreciate the extra threat from repeated and prolonged stress which adds to fatigue. For example, many hospital workers experienced such prolonged stress through the Covid pandemic that there was a marked increase in job resignations afterward. As another example, emergency workers might effectively deal with very many crisis situations before a seemingly similar situation has an unexpectedly greater impact. This highlights the importance of people taking breaks or otherwise monitoring and helping limit the impact of cumulative stress.
Compressive and Tensile Stress
Two types of stress include compressive stress and tensile stress. Compressive stress relates to force applied over a particular area. In psychological terms this might relate to having heavy work-related demands. Tensile stress relates to a force which involves a material being pulled apart. In psychological terms, this might include where a person is experiencing internal conflict, such as guilt resulting from a contrast between their behaviour and internal values. It might also include feeling torn in making an important decision.
In order to ease compressive stress, it might help to reduce our demands, including allowing ourselves more time to complete them to spread out the load. We might also draw further on social support or collaborative teamwork, as evident in the expression “many hands make light work”. If we share a certain load across many people then the amount of stress on any one individual is reduced and the strain will be less.
If we experience internal conflict in terms of conflicted values or feeling torn in making a decision, it helps to have a way of stepping back from the situation, acknowledging our conflicting feelings, and considering how we might have a more balanced or integrated perspective. In therapy situations, chairwork can be of particular benefit to help address such conflicts. Relationship therapy also helps to identify conflicts where people are pulling in different directions. It supports and encourages partners to turn toward and collaborate with each other to reduce strain in their relationship.
Identifying and Reinforcing Vulnerable Parts
Engineers consider which parts of an object are under greatest stress to redesign or reinforce those parts. Similarly, psychological therapies are designed to identify points of particular vulnerability for that individual, such as perfectionism, excessive concerns about disapproval, or lingering trauma memories. This then helps people be more targeted in their attempts to address those difficulties and bolster their resilience.
Therapy approaches sometimes vary in their emphasis on identifying strengths as opposed to vulnerabilities. For example, positive psychology typically prioritises a focus on people’s strengths. By contrast, the usual early focus of most psychotherapy approaches is to target people’s vulnerabilities or “weaknesses”. In my view, when people are struggling with more severe or prolonged psychological difficulties, it is generally most effective and efficient to target the vulnerabilities first. This is consistent with an engineering approach of first identifying and strengthening areas of vulnerability. Addressing the most pressing problems will likely gain the most benefit in reducing undue strain. Once those issues are better addressed, the focus might then shift more to drawing on and bolstering people’s strengths to support their resilience, as well as to enhance their enjoyment, meaning and quality of life.
Be like Bamboo
When facing increased psychological stress, perhaps it helps for us to function somewhat like bamboo, rather than trying to be as strong as steel or a rock. Bamboo is a relatively pliable material, which allows it to be subjected to more strain without breaking. It’s pliability also allows signs of stress to more readily visible. Bamboo will readily show at least temporary signs of yielding to a forceful wind (elastic strain), but can nonetheless withstand very considerable force before being more permanently bent out of shape (plastic strain) or breaking.
If we respond to stress like bamboo, we will recognize its impact sooner, as we will more readily show at least temporary signs of yielding to it (elastic strain). This is the equivalent of allowing ourselves to be somewhat vulnerable, rather than expecting ourselves to be unaffected by stress. Early awareness of increased stress in terms of our stress signature is protective, as it more quickly alerts and mobilizes us to manage it.
Being like bamboo would also allow us to appreciate that we might nonetheless withstand considerable force before being more permanently bent out of shape (plastic strain) or breaking. Continuing to develop stress management strategies and recognizing how we have managed with challenging situations in the past can bolster our strength and resilience.
A Point of Difference
A fundamental difference in the notions of stress and strain in engineering as opposed to psychology is that humans have a capacity for learning and insight that inanimate objects don’t. We can learn from the impact of past experience, including previous experience of stress and strain in particular situations in a way that can bolster our future resilience. If we actively consider what we learnt from previous stressful periods, along with bolstering our coping and adaptive strategies, we will often emerge from such trials with an even greater capability of withstanding various challenges in future. Wisdom can be gained. This notion is famously reflected in the words of the philosopher, Friedrich Nietzsche, “What doesn’t kill you, makes you stronger”. All cultures share this wisdom in their own variations of the archetypal theme of the hero’s journey.
Chris Mackey is a clinical and counselling psychologist with over 40 years’ psychotherapy experience. He has regularly presented at national and international scientific conferences
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