STRESS

Exercise controls the emotional and physical feelings of stress, and it also works at the cellular level to rebuild neurons

Exercise sparks the recovery process and leaves our bodies and minds stronger and more resilient to future stressful situations

The feelings of stress can span a wide emotional range, from a mild state of alertness to a sense of being completely overwhelmed by the push and pull of life. At the far end of the spectrum is the feeling of being “stressed out” — where ordinary issues take on the proportions of insurmountable problems.

Stay there too long and you develop chronic stress, which translates emotional strain into physical strain. This is where the ripple effects of the body’s stress response can lead to full-blown mental disorders such as anxiety and depression, as well as high blood pressure, heart problems, and cancer.

The way you choose to cope with stress can change not only how you feel, but also how it transforms the brain.

Exercise combats stress leaving our bodies and minds more resilient 

It’s well known that the way to build muscles is to break them down and let them rest. The same paradigm applies to nerve cells, which have built-in repair and recovery mechanisms activated by mild stress. The great thing about exercise is that it fires up the recovery process in our muscles and our neurons. It leaves our bodies and minds stronger and more resilient, better able to handle future challenges, to think on our feet and adapt more easily.

The stress response

Triggered by a primitive call to survive, the body’s stress response is a built-in gift of evolution without which we wouldn’t be here today. The response ranges from mild to intense depending on the cause. Severe stress activates the emergency phase, commonly known as the fight-or-flight response. It’s a complex physiological reaction that marshals resources to mobilize body and brain, and engraves a memory of what happened, so we can avoid it next time.

The threat has to be fairly intense for the body to get involved, but any degree of stress activates fundamental brain systems — those that manage attention, energy, and memory. If we strip away everything else, our ingrained reaction to stress is about focusing on the danger, fueling the reaction, and logging in the experience for future reference. It is only in recent years that scientists have begun to recognize and describe the role of stress in the formation and recall of memories.

The fight-or-flight response calls into action several of the body’s most powerful hormones and scores of neurochemicals in the brain. The brain’s panic button, called the amygdala, sets off the chain reaction on receiving sensory input about a possible threat to the body’s natural equilibrium. The amygdala connects to many parts of the brain and thus receives a wide array of input — some of it routed through the high- level processing center of the prefrontal cortex, and some of it wired indirectly, bypassing the cortex, which explains how even a subconscious perception or memory can trigger a stress response.

Within ten milliseconds of sounding the alarm, the amygdala fires off messages that cause the adrenal gland to release different hormones at different stages. First, norepinephrine triggers lightning-fast electrical impulses that travel through the sympathetic nervous system, and activates the adrenal gland to dump the hormone epinephrine, or adrenaline, into the bloodstream. Heart rate, blood pressure, and breathing increase, contributing to the physical agitation we feel under stress.

At the same time, signals carried by norepinephrine and corticotropin-releasing factor (CRF) travel from the amygdala to the hypothalamus, where they are handed off to messengers that take the slow train through the bloodstream. These messengers prompt the pituitary gland to activate another part of the adrenal gland, which releases the second major hormone of the stress response: cortisol. This relay from the hypothalamus to the pituitary to the adrenal gland is known as the HPA axis, and its role in summoning cortisol and in turning off the response makes it a key player in the story of stress.

Meanwhile, the amygdala has signaled the hippocampus to start recording memories and another dispatch is sent to the prefrontal cortex, which decides whether the threat truly merits a response.

The stress-and-recovery dynamic on a cellular level

On a cellular level, the stress-and-recovery dynamic takes place on three fronts: oxidation, metabolism, and excitation. When a nerve cell is called into action, its metabolic machinery switches on like the pilot light in a furnace. As glucose is absorbed into the cell, mitochondria turn it into adenosine triphosphate (ATP) — the main type of fuel a cell can burn — and just as with any energy conversion process, waste by- products are produced. This is oxidative stress. Under normal circumstances, the cell also produces enzymes whose job it is to mop up waste such as free radicals, molecules with a rogue electron that rupture the cell structure while careening around trying to neutralize the electron. These protective enzymes are our internal antioxidants.

Metabolic stress happens when the cells can’t produce adequate ATP, either because glucose can’t get into the cell or because there’s not enough of it to go around. Excitotoxic stress occurs when there is so much glutamate activity that there isn’t enough ATP to keep up with the energy demand of the increased information flow. If this continues for too long without recovery, there’s a problem. The cell is on a death march — forced to work without food or resources to repair the damage. The dendrites begin to shrink back and eventually cause the cell to die. This is neurodegeneration, the mechanism underlying diseases such as Alzheimer’s, Parkinson’s, and even aging itself. It’s largely through intensive study of these diseases that scientists have discovered the body’s natural countermeasures to cellular stress.

The stress of exercise is predictable and controllable because you’re initiating the action, and these two variables are key to psychology. With exercise, you gain a sense of mastery and self-confidence. As you develop awareness of your own ability to manage stress and not rely on negative coping mechanisms, you increase your ability to “snap out of it,” so to speak. You learn to trust that you can deal with it.

When you say you feel less stressed out after you go for a swim, or even a fast walk, you are.

Humans are unique among animals in that the danger doesn’t have to be clear and present to elicit a response — we can anticipate it; we can remember it; we can conceptualize it. And this capacity complicates our lives dramatically, says Dr. John Ratey, author of SPARK and co-founder of Sparking Life.

“The mind is so powerful that we can set off the [stress] response just by imagining ourselves in a threatening situation,” writes Rockefeller University neuroscientist Bruce McEwen in his book, The End of Stress as We Know It. In other words, we can think ourselves into a frenzy.

According to Dr. Ratey, there is an important flip side to McEwen’s point: We can literally run ourselves out of that frenzy. Just as the mind can affect the body, the body can affect the mind.