What is stress, really?
What stress actually is and isn't
First things first, stress isn't some abstract unmeasurable quantity. There are three main systems in the body that manage the stress response. All three are defined by a balance, i.e. you want a Goldilocks amount of each. When in balance, that state is called homeostasis. Most importantly, all three are linked together quite tightly.
Stressors: Your brain interprets various sensory inputs, but also thoughts as stressors. This can range from bad dreams, your boss shouting at you, stubbing a toe, to a speeding bus about to hit you. Your brain passes the bad mojo to your nervous system.
Central nervous system: Your nervous system is the wiring from your brain to your organs. It controls things like your autonomous heart-beat and semi-autonomous breathing. It knows you better than you do (or at least thinks it does) and controls a balance between fight or flight and rest and digest modes to your body. External stressors sensed by your nervous system and brain trigger changes in that balance. That change signals your endocrine system and your immune system accordingly to take action using chemicals called neurotransmitters.
Endocrine system: Stress hormones are emitted by the adrenal, pituitary, and hypothalamus. Among other things like waking you up in the morning, keeping you alert and focused, shivering when cold, they trigger your body's immune response. This same system also controls all your other hormones, like testosterone and insulin which manage the growth of your muscle and fat cells for instance. So if you mess around here, you mess up your body head to toe.
Immune system: There are many types of immune cells, that react to stress hormones to either chill or kill. This is how your body knows to build scar tissue, burn out germs with a fever, or induce nausea, or make you sleepy. It's trying to keep you alive in the face of an active threat.
How do you get stressed?
There are some pretty nuanced scientific frameworks to categorize stressors, but honestly, this is perhaps the only intuitive part of stress. You know the causes, cause everybody has them!
Mental: This is your perception of your experience that translates your thoughts, emotions, and moods into physical manifestations through your nervous system and neurotransmitters. Bad vibes lead to bad things in your body.
Behavioral: Things that upset your body's natural balance, called homeostasis, are the usual suspects in sleep, food, and exercise. There are good and bad doses of each.
Environmental: This would cover all sorts of toxins you expose yourself to, which includes the big ones like smoking and drinking, but also more subtle toxins like chemicals, radiation, allergens, molds, and other nasty stuff out there in the world.
What stress does to the body
To be clear, we need to consider the good stress responses along with the bad. We absolutely don't want to eliminate all forms of stress. We couldn't live without it. We just need to titrate the amounts and avoid chronic accumulation.
Which is a fancy way to say instant or short-term, i.e. hours to days. Good doses cause short-term hormesis, which is a dose of stress the body can recover from, and actually creates an adaption that makes you more resistant to that stress over time. Like bicep curls to blow up your guns. If you overdo it, say like a bottle of Tequila, well let's just say it isn't a good form of stress.
Oxidative stress: When you use tons of oxygen during a workout, aerobic or anaerobic, it creates waste products from your mitochondria like reactive oxygen species. If you do too much, like say run a marathon, your body will struggle to clear everything out and will cause oxidation damage in surrounding tissues.
Cell repair: Exercise actually causes damage in your cells like muscle fibers through oxidative stress, and this triggers a good type of inflammation to repair those and be stronger for the next bout.
Nervous system fatigue: The exact mechanisms of how we feel fatigued aren't well established, but it is clear that the nervous system controls the rise and fall of your heartbeat during and after exercise. By repeating this cycle more often, you increase the nervous system's control over the heart.
Meaning long-term, i.e. months to years. Most chronic stress is bad, with the exception of exercise. At the right levels, of course.
Exercise: Chronic exercise can shift the balance of the nervous system from being sympathetic dominant to parasympathetic. As we learned, that can prevent a whole cascade of bad things from developing in your endocrine and immune systems. Exercise really is the best medicine!
Oxidative stress: The same reaction that helped you recover from your killer ab crunch challenge, can accumulate in your body letting tissue damage and inflammation get out of hand. This could happen due to overtraining, i.e. not allowing for recovery, or even things like toxin buildup in your body.
Anxiety, depression, burnout: The traditionally more well-known link between stress and health is that of mental health. Once your neurotransmitters get out of whack, they stay out of whack until you change something and wreak havoc on your endocrine and immune systems like it was drunk texting. Sadly, the usual cycle involves mediation and then counter-medication, which removes the symptoms but doesn't solve the root cause.
Inflammation: In the presence of physiological or psychological stressors, your body upregulates proinflammatory cytokines, and they stick around since the stress isn't going away. Like you refuse to heal. The bad news is the cytokines start to cause problems themselves. Chronic inflammation is linked to premature aging, cardiovascular disease, and metabolic disorders like diabetes, so this stuff will actually kill you.
Weakened immune response: Once you compound these factors over time, you actually significantly weaken your body's natural armor, the immune response. You are suddenly more likely to a) get sick but also b) stay sick due to your body's inability to fight back as it should, or fight back when it really didn't need to.
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