Think of a recent time you felt stressed. Maybe it was during an argument with your spouse, or a meltdown with your kids. Maybe you were stuck in traffic and late for an important meeting. Or maybe you were lying in bed, worrying about work. Whatever the cause of your stress, your body and brain were almost certainly experiencing the same thing: boiling blood pressure, a churning stomach, tight muscles and a racing mind.
We all recognize this feeling of stress. It’s more than a mental state; it’s a full-blown mind-body response. When stress takes hold, the brain is bathed in chemicals that heighten our senses and focus our attention, making it impossible for us to think about anything else. The sympathetic nervous system gets a jump-start, and stress hormones like adrenaline and cortisol make us feel even more wired. Glucose and fats flood the bloodstream, and our cardiovascular and respiratory systems rev up, all to give us the energy we need to deal with the stress.
These changes would make sense if we were running for our lives or rescuing our child from a fire. But when everything from taxes to television news triggers a reactive response, stress becomes toxic. Chronic stress increases the risk for a wide range of health problems, in large part because the body’s response to stress adds up over time (McEwen 2006). Chronic inflammation and sympathetic activation contribute to autoimmune disorders, chronic pain and cardiovascular disease. Elevated blood glucose and fat levels raise the risk of insulin resistance and diabetes. Chronic exposure to stress hormones suppresses the immune system, kills off brain cells and promotes obesity. When any unwanted physical or psychological condition is present, chances are that stress plays a role.
And yet, not everyone is equally susceptible. Some people seem to be protected from the worst effects of stress. These resilient folks handle stress better and recover from stress more quickly. Science is beginning to reveal the secrets of stress resilience and to learn what it looks like in the brain and body. It turns out we can measure stress resilience in the heart, the nervous system (which includes the brain) and even our DNA. We can also train resilience—even in the face of chronic stress.
The Resilient Brain
Psychological stress begins in the brain when we perceive a threat. The brain triggers the body’s fight-or-flight stress response and directs the process of stress recovery. It should be no surprise, then, that the search for the biology of stress resilience must include the brain.
Three regions of the brain control the stress response: the amygdala, which detects threat and triggers the fight-or-flight response; the prefrontal cortex, which helps us deal calmly with stress, and can prevent or shut down a fight-or-flight response; and the hippocampus, which supports stress recovery (McEwen & Gianaros 2010).
Neuroscientists now know that chronic stress can change these brain regions in a way that makes us more sensitive and less resilient to stress (Ganzel, Morris & Wethington 2010; McEwen & Gianaros 2010). For example, high levels of stress hormones are neurotoxic to the prefrontal cortex or hippocampus, can reduce the connections between brain cells and can even kill brain cells. As these areas weaken, the brain gets worse at managing stress. Chronic stress has the opposite effect on the amygdala, the brain’s threat detector. Repeated stress can actually make the amygdala grow, increasing connections between brain cells and heightening cell excitability. This makes the brain even more reactive to stress. These brain changes are associated with, and likely contribute to, a range of stress-related disorders, from depression to cardiovascular disease and accelerated aging (Ganzel, Morris, & Wethington 2010).
How Exercise Changes the Brain
Exercise has shown tremendous promise as a neuroprotective intervention (Fleshner et al. 2011; Head, Singh & Bugg, 2012; McEwen 2012). Research has identified several ways that exercise protects the brain from stress—and even reverses the effects of chronic stress on the brain (Stranahan & Mattson 2012; Rothman & Mattson 2012). Exercise increases brain-derived neurotrophic factor, which maintains brain health, supports brain growth and combats the negative effects of stress. Exercise seems to enhance BDNF specifically in the prefrontal cortex and hippocampus, the two regions most susceptible to stress-related damage. Exercise also triggers the brain’s self-repair processes, which may help reverse any stress-related neurotoxicity. Finally, exercise activates the brain’s stress-calming system, releasing a neurotransmitter called GABA, which helps restore balance in the autonomic nervous system. When we exercise regularly, we naturally engage all of these neuroprotective processes. Over time, exercise can create a “stress-resistant” brain that is less sensitive to threat and recovers more quickly from stress (Fleshner et al. 2011).
Finding the Right Dose of Exercise
Several recent reports have focused attention on the potential health risks of extreme training. While moderate exercise improves cardiovascular health, intense workouts lasting longer than 2 hours can cause temporary damage to the heart, and over time, can lead to dangerous remodeling of the heart’s structure (O’Keefe et al. 2012; O’Keefe & Lavie 2012). A major review of exercise’s effects on the immune system found that moderate exercise enhances immunity, but higher levels suppress it and increase the risk of illness and infection (Walsh et al. 2011a).
The same pattern holds true for stress resilience. While moderate physical activity is associated with lower levels of stress hormones and faster recovery from stress, the protective effect disappears with intense and prolonged training. Exercise becomes another form of chronic stress (Walsh et al. 2011b). The overtrained athlete may develop an exaggerated stress response to exercise, fail to recover between workouts, and show chronically elevated levels of stress hormones. When this happens, exercise amplifies rather than protects against the health risks of psychological stress.
Of course, there are many reasons to work out, and some goals require intense training. If this is true for you or your clients, it’s important to look for ways to support not only physical workout recovery but also general stress management (Walsh et al. 2011b). Mind-body practices, sleep habits, diet and strategies from positive psychology can all play a role in reducing psychological stress and improving resilience.
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