The Stress Response

Historically, there has always been a view that there is a link between physical and mental well-being and vice versa. A great deal of research shows relationships between various aspects of health, including physical and psychological well-being, over the years. There is an ever-increasing evidence base from multiple areas of research suggesting that physical and mental well-being are inextricably linked. However, numerous factors affect health, and one could argue that there are multiple types of health or wellness.

These types of health and well-being are interrelated, and the relationships are far from fully understood.  "Stressors" can take many forms and affect every kind of health and, thus, overall health. Research has demonstrated significant links between various aspects of health. Hence, a pure BioPsychoSocial model of health is a little too simplified. The human stress response also has relevance in developing chronic pain and treating patients with chronically painful conditions. See the article on Chronic Pain for further details on aspects of such conditions and treatment.

Elite Sports and Elite Military units have always appreciated the relationships between physical health, psychological welfare, and superior performance. Such organisations have invested considerable amounts of time, finance, research, and effort to ensure that they recruit, select, train and retain the very best candidates. In the case of the worlds elite military services, this includes individuals who are the best physically and psychologically suited to the demands of such a career. Diversity also plays a considerable part in the effectiveness of such Elite teams, with the selection of individuals coming from all walks of life, provided that they meet high and exacting physiological and psychological standards set by the selection course(s).  Industry can learn a great deal from these elite level individuals and top performing teams. Such, organisations and cultures continually strive to push the limits of human and performance daily, or as one now infamous British Military Unit would say, 'the unrelenting pursuit of excellence.' Even slight enhancements in performance can prove critical regarding winning and losing, or actual life and death. It is also of paramount importance that organisations get a good return on their investment. Such organisations fully understand the value of their people and the level of investment in said people. Hence, utilisation and career longevity from these elite level personnel is paramount and not merely from a return on investment perspective.  Not only does physical and mental wellbeing have a direct impact on performance, but it is relatively easy to see the links between physical and psychological wellbeing.

As remarkable and versatile as the human body is, the body does make various trade-offs. The human body has some extremely sophisticated systems, yet these do not all need to be running concurrently and all the time. Indeed, each system or process will utilise various resources, and the human body only has finite resources and operates efficiently. Historically, multiple food sources would have been in short supply, yet each bodily function consumes energy, various nutrients, and water. Examples of efficiency trade-offs include how the brain operates, how we make decisions, how tissues within the body repair and how we deal with stress. Hence, the human body manages resources to be as efficient as possible by moderating how various systems operate and by turning systems on and off accordingly.

The Sympathetic Nervous System (SNS) is responsible for multiple life-sustaining functions, including threat assessment and the fight, flight and freeze response. The SNS continuously works at a base level, maintaining homeostasis, even when the Parasympathetic Nervous System (PSNS) operates. Sensory inputs and information are continually sent to the brain for processing via the CNS. The control of essential life support functions and homeostasis happens subconsciously. We do not have to think about making our heartbeat, breathing, or maintaining other vital life-giving actions, such as blood PH values, blood glucose levels or temperature regulation. Such critical aspects of self-maintenance have a "normal or safe" operational level, and relatively small deviations from these normal "safe" levels can prove fatal. Hence, all these functions are taken care of subconsciously, and the vast majority of these functions cannot be controlled consciously by us.  Various sensors within the body are constantly being monitored, with the body making any necessary adjustments on the fly to maintain homeostasis. There are also sensory inputs we are far more familiar with or know are working. We are all familiar with the five basic senses; touch, sight, smell, hearing, and taste. If any of these primary senses detect anything the brain perceives as a threat, then the Sympathetic Nervous System activates.  The activation of the Sympathetic Nervous System is a highly efficient and effective ancient survival mechanism, commonly referred to as the "fight, flight or (freeze)" response.  The stress response involves sending sensory information to the amygdala from one or a number of the "primary" sensors. The amygdala is a small part of the brain, located near the brainstem and involved in emotion processing and is part of the limbic system. If the amygdala interprets and "perceives" inputs from the primary sensors as a threat, then a distress/alarm signal is instantly sent to another part of the brain, the hypothalamus. One can view the hypothalamus as a control centre based on the far-reaching effects it can have on the body. There are two parts to the "fight, flight or freeze" response. Firstly, the hypothalamus activates the initial "fight, flight or freeze" response via the autonomic nervous system. The hypothalamus instructs the adrenal glands to release adrenaline and norepinephrine into the bloodstream.

The hormonal release produces changes throughout the body, including shutting down the Parasympathetic Nervous System function. If one has a choice of "fighting" or running away from a threat, then all resources need to be aimed at those activities/behaviours and not digesting food, resting or procreating. The initial release of adrenaline and norepinephrine into the bloodstream creates multiple changes within the body, including increasing heart rate, respiration, blood pressure, muscle tension and releasing stored nutrients and energy from tissues within the body. The increase in oxygen and nutrients within the blood supply to the brain heightens all five of the primary senses. The increase in muscle tension helps to protect the body from potential physical harm and reduces blood flow to the superficial tissues (skin). The tensioning or armouring of the bodies tissues also impacts tensional and compressive forces throughout the body (Biotensegrity) see article. Reducing blood flow to the superficial tissues would minimize blood loss should the person or animal get injured while dealing with imminent danger. The increase in oxygen, nutrients and energy supplies within the blood also primes the musculoskeletal system to "fight" or "flight" (run away) from danger. The "fight, flight or (freeze)" response is so efficient that the human body has already reacted subconsciously before we consciously register a threat. The subconscious process explains why people can often get out of the way of danger before getting injured and being aware of the danger. Prolonged exposure to stressors not only affects biotensegrity, but the tissues within the body can adapt Soft Tissue Adaptation to these changes in forces.

The second part of the “fight, flight or (freeze)” response is relatively instantaneous but slightly slower than the initial reaction. It enhances the primary response and keeps the body in a high state of readiness. The hypothalamic-pituitary-adrenal axis is responsible for the release and control of levels of cortisol in the bloodstream via a negative feedback loop. The hypothalamus releases corticotropin-releasing hormone (CRH), which makes the pituitary gland release adrenocorticotropic hormone (ACTH). The adrenal glands detect ACTH and release cortisol into the bloodstream.

Historically there would have most likely been some form of physical activity straight after or shortly after initiation of the “fight, flight or (freeze)” process, hopefully resulting in personal survival. Once a perceived threat to life has passed, sensory inputs to the brain allow the brain to return the Sympathetic Nervous System to running at a base level. Blood cortisol levels would then be able to reduce via the negative feedback loop. However, this process is inhibited during the “fight, flight or (freeze)” response, preventing cortisol levels from normalising. Under normal circumstances, the detection of high levels of cortisol in the bloodstream blocks the release of CRH and, thus, the release of ACTH. The result is a decrease in cortisol within the bloodstream. This situation then continues to inhibit the Parasympathetic Nervous System from functioning normally.

The Parasympathetic Nervous System plays a crucial role in calming the body after a perceived threat has passed. The PSNS is responsible for functions involving “rest and digest” and or “feed and breed” and is also part of the Autonomic Nervous System (ANS). The PSNS is responsible for controlling many bodily functions essential to physical and mental health and the continuation of the human species. Besides slowing the heart rate and reducing blood pressure after initiating the “fight, flight or (freeze)” response, the PSNS also plays a major role in regulating other functions. Other functions include the regulation of digestion, urination, defecation, sexual arousal, menstruation, memory formation and repairing tissues and structures throughout the body. The metabolic processes regulated by the PSNS can only function when not inhibited by the SNS during a “fight, flight or (freeze)” response.

Historically, the initiation of the ancient "fight, flight or (freeze)" response would relate to an imminent threat to life. One would then have had to "fight" or "flight" (run away) to survive. If one survived and the threat to life had passed, the SNS would return to running at the base level again. Either way, the stress response resulted in physical activity after initiation. The time it can take for SNS to return to running at base level after starting the stress response can vary greatly and take anything from 30 minutes to a couple of days. Research and thinking suggest that such variations are likely down to many factors including, but not limited to, genetics, health/fitness, diet, training and previous experiences. Hence, historically the chances of the SNS consistently activating would have been slim. Hence, the functions of the PSNS would have been able to operate regularly. However, the modern world we live in today is hugely different from that of our ancestors. Today's modern world has very different stressors, which are rarely life-threatening, yet the body's primaeval response to stress is the same. Furthermore, the stress response can be initiated multiple times daily, even for extended periods. The PSNS cannot regulate critical metabolic processes if the stress response is continually activated.