How the Body Responds to Stress

“For 99 percent of the beasts on this planet, stress is about three minutes of screaming in terror after which it’s either over with or you’re over with. And we turn it on for 30-year mortgages.” 

—Robert Sapolsky

The abrupt feeling of discomfort that hits us when met with adversity. The dry mouth and jolt in heart rate that assault us before a high-stakes conversation. The tightening in the throat when you realize you’ve made a mistake.

That’s stress.

And contrary to popular opinion, it’s not always bad.

Short-term mild stress and the subsequent physiological response it provokes in us can be beneficial. Stress alerts us to possible danger and equips us to escape or manage it. The problem is when it becomes chronic.

For those of us who have access to shelter, food, and basic psychological safety, immediate life-threatening stressors are rare. But that doesn’t mean we’re not stressed.

Perceived loss of control over our lives, performative social media, 24/7 access to unlimited information, and no delineation between work and home all play parts — and unlike an intense but swift encounter with a saber-toothed tiger, these stressors permeate our daily lives.

The good news is that we can mitigate the effects of these stressors. To do so, it’s helpful to first understand how the body responds to them.

Stress manifests in two broad forms: physical and psychological.

Examples of physical stressors are pain, injury, illness, intense physical labor, extreme temperatures, and lack of adequate nutrition. Psychological stressors may include relationship conflict, unrealistic expectations of ourselves or those imposed on us by others, financial strains, anxiety about our health, and the hugely overlooked exposure to traumatic events.

Stress kicks the sympathetic nervous system, one of two branches of the autonomic nervous system, into gear. Responsible for the “fight or flight” response, the sympathetic nervous system interacts with the hypothalamic-pituitary-adrenal (HPA) axis to control the body’s stress response, heightening responses that can be beneficial in that period of stress and dampening others that are less important and take up bandwidth.

The cascade of events results in the release of adrenaline and noradrenaline — epinephrine and norepinephrine — among other hormones. These chemicals have impacts on different receptors resulting in different outcomes. Among them are dry mouth, an increased heart rate, narrowed focus, and increased blood flow to the extremities to allow for fast movement.

We also experience an increase in blood glucose — which fuels that fast movement — a subtle change in blood pressure, a change in skin temperature, and an enhanced immune response, indicating that stress in appropriate time frames is good for our immune system.

The yin to the sympathetic nervous system’s yang is the parasympathetic nervous system. Also known as the “rest and digest” response, the parasympathetic nervous system governs the body’s ability to relax. The vagus nerve is its main component, and it communicates with the brain, heart, and digestive system to regulate heart rate, blood pressure, digestion, and immune response, among other functions.

When the parasympathetic nervous system is in command, things slow down. We relax, allowing our bodies to focus on things like digesting food and reproduction. Our heart rate and breathing slow. Cortisol, adrenaline, and other stimulating chemicals are no longer front and center. It’s this state which allows for productive sleep.

A balance between the systems is required to keep us on an even keel. During acute stress, this fine balance is tipped one way, and that is in the direction of immediate action. Unfortunately, the prolonged stress and chronic illness so prevalent in our society keep the scale tipped in favor of the sympathetic response, turning what would in the short or medium term be a beneficial response into a harmful chronic issue.

But what about exercise? Doesn’t that act as a stressor?

It depends on what you’re doing. Going for a walk in a beautiful green park can activate the parasympathetic nervous system, for example. But high-intensity exercise or exercise requiring prolonged metabolic demand does indeed activate “fight or flight” mode.

If you wired someone up to lots of machines and asked them to do the workout Barbara, you’d notice a rise in blood pressure, heart rate, and respiratory rate. Blood glucose levels would rise quickly as the liver anticipates how much energy is required for the task at hand.

These are healthy sympathetic responses to exercise. They help us get the job done and then retreat when we don’t need them anymore. In fact, this small amount of stress repeated regularly results in adaptations to our physiological responses. Exercise, in effect, trains our stress response.

CrossFit is elegantly designed with this in mind, and good programming takes all of this into account. We don’t go all out all the time, and we shouldn’t! A well-written CrossFit program features workouts that challenge different energy systems in multiple modalities with rest days built in.

Persistent activation of the sympathetic branch of the nervous system is problematic, however. It results in sleep issues and difficulty accessing the appropriate fuel source, influences the storage of fat, and can lead to chronically elevated blood sugars and insulin levels.

The last two of these things are the foundation of many of the chronic diseases impacting lifespan and healthspan — our ability to live long and live well. Heart disease, Type 2 diabetes, cancers, and neurodegenerative diseases such as dementia are underpinned by this insulin-resistant state.

But we have the power to do something about it. Changes in diet, lifestyle, and dedicated stress-management tactics can prevent and even reverse the negative consequences of chronically elevated stress.

Stay tuned for Part 2 of this two-part series to learn how to regulate the stress response in real time and rebalance the nervous system.

About the Author: Dr. Rini Chatterjee (she/her) is a general practitioner with more than 20 years of experience working in the National Health Service in the United Kingdom. She has post-graduate qualifications in diabetic health and a special interest in optimizing metabolic function. Dr. Chatterjee has appeared numerous times on U.K. radio and TV speaking on a range of medical topics but always advocating for health to be considered in the most holistic way possible. Her approach to practice always starts with what she considers to be the foundations of health: nutrition, movement, sleep, and connection. She is an active member of her own CrossFit community and has been a CrossFit athlete for nine years. She obtained her  CrossFit Level 1 Certificate at the CrossFIt Home Office in 2019. Follow her at @resilience_health.