Category Archives: Exercise & mental health

Reverse the Impact of Stress on the Brain with Exercise

Departing the 2010’s, feelings of stress and worry among Americans were the highest they had been all decade and among the highest in the world [1]. I doubt that drops any jaws. We are a bit obsessed with stress – many trying to rid ourselves of the brute through everything from mindfulness and meditation to yoga retreats and medication. I love the work by Dr. Susan David, who has concluded that all of this energy expended to ‘rid ourselves of stress’ can actually make a person more stressed (dubbed type II stress). Oh, the irony!

Stress is an inescapable aspect of our lives, and it is undoubtedly useful in short-term fight-or-flight situations, helping us better mobilize resources like glucose and oxygen. It’s the prolonged and unrelenting variety of stress that comes at a cost to the brain. In particular, a robust field of research has found that chronic stress shrinks the hippocampus [2, 3]. This region has long been implicated in learning and memory hippocampus_free licensure(episodic & spatial) [2, 4]. As a powerful illustration, atrophy in the hippocampus is the hallmark of Alzheimer’s disease. It is one of the most susceptible brain regions to cell death, and it may be particularly vulnerable to the impact of long-term stress because it has a high concentration of cortisol receptors [5].

So, that’s the bad news. Here’s the good: because the hippocampus exhibits so much adaptive plasticity, the effects produced by chronic stress are largely reversible. Better still, there is a free and readily accessible intervention that can dampen and even reverse these effects. I’ll give you one guess.

Most people have an anecdotal appreciation for the benefits of exercise on stress and get a feel-good buzz after a bout of exercise. What is often underappreciated is that exercise reaps very tangible anatomical and physiological benefits to the brain.  Cue my favorite study [6].

One hundred and twenty older adults were recruited and randomly assigned to 3 days a week of either moderate-intensity aerobic exercise or stretching/toning (control).*  After one year of this intervention, MRI scans showed a 2% increase in hippocampal volume for the aerobic exercise group (see graph)[6]. Exercise grew brains. Unsurprisingly, but still remarkably – the  hippocampal growth corresponded to improved memory function.

Erickson_graph 6.35.41 AM

Notice in the figure how the red line (stretching/control group) slopes down? These data support previous research showing a 1-2% decline in hippocampal volume each year in older adults, free of dementia [8]. That trajectory is inverted with the exercise group (blue line). Getting out the door for a walk 3 days a week effectively reversed age-related loss in the hippocampus by 1 to 2 years. Powerful stuff, exercise.

Now, back to stress. While there haven’t been any exercise interventions in people that look specifically at reversing the effects of stress, it doesn’t take a huge leap of fate to connect the dots here. We know chronic stress shrinks the hippocampus while exercise grows it.** Still, I like to be persuasive, and findings from a recent study in mice is just that.

Researchers at BYU had one group of mice run on wheels (covering ~5k day), while the other group remained sedentary [9]. Half of each group was also exposed to stressful situations – swimming in cold water or walking on an elevated platform. They then looked in the hippocampi of mice to assess a process called long-term potentiation (LTP). Memory formation and recall are most effective when connections between neurons are strengthened over time. LTP is a measure of this connectivity, and ultimately memory.  In the sedentary group, researchers found chronic stress weakened the synaptic connections between neurons, decreasing LTP. The mice allowed to run while exposed to stress had significantly higher LTP, and they performed better on a memory test (radial arm maze) [9]. The research team concluded, “exercise is a viable method to protect learning and memory mechanisms from the negative cognitive impact of chronic intermittent stress on the brain.”

In terms of how exercise supports the hippocampus – we believe it is a combination of increased blood flow to the brain and hippocampus [10] as well as through increased production of BDNF [6, 9, 11]. Brain derived neurotrophic factor (BDNF) is essentially a growth factor for neurons…miracle grow for brain cells.

Ridding ourselves of all the stressors in our lives is not a particularly practical option for most of us. Yet, the negative toll that stress can take is not a phenomenon beyond our control. I think that is downright empowering. So, transitioning into this next decade, resolve to move for your physical health, move for your mental health, and move for your brain health.

*Noteworthy – both groups in the study attended the same number of exercise sessions and therefore had an equal amount of social interactions. This is important because human interactions also have very real benefits on brain function [7] and may be less frequent in the older adult population.  In other words, exercise appears to protect our brains in a way that other interactions cannot. This appears to be true, even if you start moving in your 70s.

**Aerobic training grows brain regions other than the hippocampus. Another exercise intervention in older adults found increased gray and white matter volume in the prefrontal cortex after 6-months [12]. This region is instrumental to executive control functions.


[1] Chokshi, N. (2019, April 25). Americans Are Among the Most Stressed People in the World, Poll Finds. The New York Times.  Retrieved from

[2] Conrad, C. (2010). A critical review of chronic stress effects on spatial learning and memory. Prog Neuropsychopharmacol Biol Psychiatry 34(5): 742-755.

[3] Conrad, C. (2008). Chronic stress-induced hippocampal vulnerability: the glucocorticoid vulnerability hypothesis. Reviews in Neurosciences 19(6): 395-411.

[4] McEwen, B., Nasca, C., Gray, J. (2016) Stress effects on neuronal structure: hippocampus, amygdala, and prefrontal cortex. Neuropsychopharmacology Reviews, 41, 3-23.

[5] Kino, T. (2015). Stress, glucocorticoid hormones, and hippocampal neural progenitor cells: implications to mood disorders. Frontiers in Physiology 19.

[6] Erickson et al. (2011). Exercise training increases size of hippocampus and improves memory. Proceedings of the National Academy of Sciences, 108 (7): 3017-3022.   

[7] Hari, R. & Kujala, M. (2009). Brain basis of human social interactions: from concepts to brain imaging. Physiological Reviews, 89, 453-479.

[8] Raz N, et al. (2005) Regional brain changes in aging healthy adults: General trends, individual differences and modifiers. Cereb Cortex, 15, 1676–1689.

[9] Miller, R. et al. (2018). Running exercise mitigates the negative consequences of chronic stress on dorsal hippocampal long-term potentiation in male mice. Neurobiology of Learning and Memory, 149. DOI: 10.1016/j.nlm.2018.01.008

[10] Burdette J., et al. (2010) Using network science to evaluate exercise-associated brain changes in older adults. Front Aging Neurosci 2:23.

[11] Vaynman S., Ying Z., Gomez-Pinilla F. (2004) Hippocampal BDNF mediates the efficacy of exercise on synaptic plasticity and cognition. European Journal of Neurosciences 20:2580–2590.

[12] Colcombe S., et al. (2006) Aerobic exercise training increases brain volume in aging humans. J Gerontol A Biol Sci Med Sci, 61, 1166–1170.



Exercise to Fend Off Daily Stress

At any given point in time, most people are feeling stressed out about something. Unfortunate though it is – having stress in your daily life is often unavoidable. But being stressed is something within your control. stress_zebra stripes

One way to exercise that control is to — exercise. A single bout of exercise may offer protection against the emotional events and stress that we encounter later in the day.  That’s the conclusion of new research from the University of Maryland (yes, I’m biased, but this is good work). The immediate ability of physical activity to boost mood and ease anxiety is well established. However, this study found that the stress-busting effects of exercise endure after we’ve left the gym, and more importantly, in the face of subsequent psychological stress. In other words, getting up and moving may make us more resilient to the effects of stress.  If we know there’s no escaping a stressful event, we can at least prepare ourselves to better handle it by breaking a little sweat earlier in the day.

The study, published in the February issue of Medicine and Science in Sports, measured how anxiety levels in college students differed following 30 minutes of moderate intensity cycling (described as “somewhat hard”) and 30 minutes of seated rest. To assess anxiety, students completed the State-Trait Anxiety Inventory (STAI). This tool essentially gathers a snapshot of a person’s emotional state by having them rate subjective feelings of tension, apprehension, nervousness, and worry. On one day, participants answered questions on the STAI before exercise, 15 minutes after exercise, and finally – after viewing a series of images, known to provoke emotion. These include highly arousing unpleasant, pleasant, and neutral pictures. On a separate day, students followed the same procedure with the resting condition.

Researcher J. Carson Smith found that once the emotional picture-viewing period ended, anxiety state rose back up to baseline levels following the resting condition but remained low following the exercise. As expected, exercise and seated rest were equally effective in reduced anxiety levels initially. Smith explains, “Even though you can feel better by just sitting and doing nothing, you’re probably not doing yourself as much good as you would be if you were to exercise to receive that same anti-anxiety effect.”

Americans between 18 and 33-years-old – the so-called Millennials – are more stressed than the rest of the population, according to a recent report from the American Psychological Association.  However, they are also more likely than other generations to turn to sedentary activities to cope with this stress.  Listening to music was most widely reported (59% of young adults), but playing video games, surfing the Internet, and eating were also common ways of managing daily stress. These findings should encourage people to adopt physically active coping mechanisms in lieu of such sedentary ones.

It is still unclear exactly how long the anxiety-reducing effects from exercise last, but this study found benefits on mood approximately one hour after the exercise stopped. The duration of these effects, as well as the intensity and length of exercise needed to optimize them, has also yet to be established.

It is popular belief that endorphins are to thank for these effects, but Smith cautions that very little evidence supports a role of endorphins here. Instead, he hypothesizes that “the neural networks related to reward and motivation are being modulated and tuned such that there is a resistance to the effects of the accumulation of stress.” The use of neuroimaging will shed more light on whether and how these neural networks, or interconnected groups of brain cells, may be systematically impacted by exercise.

Chasing the Blues Away

We are bombarded with information that partitions exercise and movement into isolated entities. We learn about heart rate zones, optimal step counts, and the strengths and limitations of maximal oxygen consumption (VO2max). We analyze power output and revolutions per minute, and critique stride length and leg turnover.  Yet, what ultimately brings so many of us back to the physical activities of our choosing is simply the fact that they make us feel good.


Indeed, the ability of exercise to lift spirits is quite profound and well established in the scientific literature.  There is now evidence that both aerobic and anaerobic exercise (namely moderate-intensity weight lifting) have the ability to significantly increase positive feelings, energy, and calmness, while reducing negative emotions and tiredness.  Yet, how is it that moving our bodies has any influence at all on our psychological state?

Numerous theories have surfaced over the years to account for the beneficial effects of exercise on mood.  Some have a psychological basis, while others stem from more biological roots. I’ve highlighted some of the mechanisms below that have received the most support from human and animal studies. These same theories also explain how exercise can reduce symptoms of chronic mood disorders, like depression.

Biological mechanisms

  • Elevated Endorphins:  There is significant evidence to show that endorphins are secreted as a result of exercise.  The word endorphin comes from endogenous + morphine, which loosely translates to internally produced pain-killers.  While these chemicals do not act directly on the brain (cannot pass blood-brain barrier), they do have a calming effect in both humans and animals. In support of this mechanism, several studies have found that when endorphins are blocked, exercise does not have the same ability to relieve stress and anxiety.  Decreased endorphin levels may also explain why habitually active people often become irritable and restless when deprived of exercise.  ahem.
  • Monoamine Hypothesis: Monoamines refer to a group of neurotransmitters that include norepinephrine (NE) and serotonin (5-HT).  Common anti-depressant drugs (Prozac, Zoloft, Paxil, etc.) function by regulating the release of these chemicals in our brains.  Substantial research suggests that physical activity modifies the release of NE and 5-HT in much the same way, making  these neurotransmitters more readily available in synapses.
  • BDNF Hypothesis: This theory primarily speaks to the long-term effects of exercise and may be especially significant in explaining how exercise can help depression. Brain-derived neurotrophic factor (BDNF) promotes neural growth and generally works to keep neurons healthy.  Some have described it as “miracle grow” for the brain, and it is key to many of the topics I blog about.  It is relevant here because BDNF also has antidepressant effects.  Both antidepressant drugs and exercise increase levels of BDNF in the hippocampus.  This region is classically associated with learning and memory, but has also been found to play a role in depression.  More on these important relationships later!
  • Other biological theories include the reduction of cortisol (a stress hormone) and better regulation of the hypothalamic-pituitary-adrenal (HPA) axis.  These have strong implications for mood, but more directly impact stress and anxiety.

Psychological mechanisms

  • Sense of Mastery and Self-efficacy:  Because exercise is often viewed as a challenging activity, the ability to commit to it on a regular basis often results in a sense of control, accomplishment, and satisfaction.  Merely setting fitness goals can also fuel a sense of purpose.  These can all contribute to both immediate and long-term boosts in mood.
  • Distraction:  Exercise can serve as a diversion from negative thoughts and other unfavorable stimuli (overflowing inboxes, screaming children…).  By forgetting our worries and focusing on our physical movements, we can temporarily alleviate stress and break cycles of unconstructive thinking.
  • Exposure to Nature:  Physical exercise often gives people a reason to get outside, and as discussed in my last entry – doing so can positively impact mood states.
  • Social Factors:  Interacting with others is important for our overall mental well-being. While some prefer the solitude of exercising alone, exercising with others can foster a reciprocal sense of support.  You may help another reach their fitness and performance goals, and someone else may do the same for you. An additional benefit of exercising with people is that you are less inclined to skip a workout if another is depending on you to be there.  Unsurprisingly, this increased adherence to exercise equates to more of it!

Most likely, the benefits of exercise on mood result from a combination of many of these theories, as well as underlying genetic factors.  Regardless of how exactly it is that exercise makes us feel good, I suspect most of us are just glad that it does!  There may be hope for Eeyore yet.

Comments and questions always welcome!

Key References:

Go outside and play

As the days grow shorter and colder, many of us will resign ourselves to fewer outdoor activities.  But, fighting the lethargy of winter months and getting outside may do more than just boost vitamin-D and combat seasonal affective disorder.  Moving through a natural environment has been shown to enhance attention and memory, relieve stress and depression, and boost immunity.

The therapeutic benefits of being outside may partly stem from alleviating what’s termed directed-attention fatigue, or essentially an overworked prefrontal cortex.  In a typical multi-tasking, computer-centric day, your prefrontal cortex is constantly helping you to focus attention, tune out distractions, and shift from one task to another – and back again.  A growing body of research supports the idea that spending time in nature provides some cognitive downtime and helps to restore or refresh these cognitive capacities.  This notion has led to an entire field of cognitive science known as Attention Restoration Theory (ART).

A prominent study on ART was released in 2008 by a team of scientists from the University of Michigan.  It revealed that adults performed 20 percent better on tasks of attention and working memory after a 50-minute walk in a park, compared to a walk in a noisy urban setting.  In contrast to natural environments, the authors surmise that urban environments are less cognitively restorative because they are filled with mental stimulations, many of which demand our directed attention (e.g., to avoid getting hit by a car).  A 2012 study by this same team of scientists showed similar cognitive benefits in patients with clinical depression.  Attention and memory benefited more so from the nature walk; however, mood was lifted by walking – regardless of the setting.  This is good news for those who may not have easy access to green spaces (more on exercise and depression later!).

Preliminary work by Dr. Jason Duvall (also at University of Michigan) suggests that to most benefit from exercising in nature, you really need to be present in it.  He suggests that heart-rate monitors, iPods, or GPS devices can all subtly alter the experience of being outdoors.  If you are constantly dialed in to a device and addicted to its output, you are not allowing yourself the same cognitive downtime that you would without it.

It almost seems that exercising in the great outdoors can elicits a type of meditation.  I think this is one place where endurance-type activities have an enormous advantage.  You just can’t get “lost in the moment” during a tennis match, cross-fit workout, or game of pick-up basketball.  Be it running, walking, hiking, or biking, the repetitive nature of the movements can transport you to a calm, near zen-like “zone” where you are totally caught up in the here and now.  For me, this is never more true than when I’m running through wooded trails.  It turns out; this is precisely the premise behind “mindfulness training.”  Mindfulness training essentially teaches the mind to be attentive to the present and not dwell in the past or project to the future.

Because of this link between exercise and mindfulness, a new study in the Frontiers in Human Neuroscience caught my eye this week.  Using fMRI, the authors found that 8-weeks of mindfulness training can reduce the amygdala’s response to emotional stimuli.  The amygdala is a region deep within our temporal lobes that plays a key role in processing emotions. Abnormalities here have been linked to anxiety, depression, and phobias.  So, they essentially found that by regularly engaging in mindfulness, we can provoke enduring, beneficial changes to how our brains process emotions in everyday life.  Interestingly, mindfulness training has even been shown to boost immunity by reducing pro-inflammatory gene expression.  How’s that for a mind-body connection?

The mind aside, Dr. Miyazaki and his colleagues in Japan have unearthed some fascinating physiological changes that stem from being in nature. Walking through natural environments for just 15-20 minutes can lower pulse rate, decrease blood pressure, and lower sympathetic nerve activity (responsible for the fight or flight response).  It also seems that it can physically ease stress, as concentrations of cortisol (a stress hormone) were nearly 13 percent lower after the short outdoor walk.  This group has even found benefits of forest walking on the expression of certain anti-cancer proteins and the immune system.

As winter kicks into full gear, you might reconsider hopping on the treadmill or trainer again and bundling up for a dose of nature instead.  You might even try leaving those gadgets behind.