We know that exercising is good for the brain. But now that we understand why, we can say what kinds of workouts maximise the brain-boosting powers of physical exertion.
IN JANUARY, I set myself a resolution: to master the humble chin-up. I have never had much upper body strength, and I knew it would be hard, but that is OK, I thought, because I am not doing this to get stronger or fitter. I am doing this for my brain.
Like a lot of people, I used to exercise to stay physically fit. But a few years ago, while writing my book Brain Power: Everything you need to know for a healthy, happy brain, I dug into the literature on exercise and the mind. What I discovered changed my relationship with exercise forever.
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It is no secret that exercise is good for the brain as well as the body. But the past decade has seen an explosion of research into just how transformational it can be, whether it is improving children’s academic performance, boosting mood and memory in adults or even protecting us from cognitive decline. “It seems to be one of the most important things you can do for the brain,” says David Lubans at the University of Newcastle, Australia. “I think much less about the physical benefits. It’s all about feeling good and optimising my brain functioning.”
Scientists like Lubans are now turning their attention to how and why exercise has such powerful effects on the mind. What they are finding is teasing apart what really works and showing us how we can best capitalise on the brain-boosting powers of physical exertion.
One of the first pieces of evidence that linked exercise and the brain came in the 1990s, when geneticist Fred Gage found that exercise could lead to the growth of new brain cells in mice. Since then, studies have shown that exercise produces chemicals that make it easier for new brain cells to communicate and that it is one of the few things that can stimulate new brain cell growth in humans too, particularly in areas of the cortex vital for learning, memory and mood.
Mood is a good place to start if you want to see how exercise can impact the brain. As any regular exerciser can attest, moving the body provides an instant tonic for the mind. Even a single session can leave people feeling more positive for several hours, and more energetic.
When it comes to mental health conditions, things are less straightforward. There is strong evidence that exercise is an effective treatment for mild and moderate depression, especially in adolescents. But in adults, results are mixed. There are also questions about how much exercise is needed to experience the benefits. Is exercise even a universal medicine? Or is it more like a medicine cabinet, with different people needing a specific type and dose?
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| Exercising improves children’s behaviour in class and should be incorporated into the school day Geber86/Getty Images |
To find out more, Sammi Chekroud at the University of Oxford and his colleagues analysed information from 1.2 million people in the US, collected over several years by the US Centers for Disease Control and Prevention (CDC). The results were staggering. Compared with people who didn’t exercise, those who did had experienced 43 per cent fewer days of poor mental health in the past month, and the effect was larger in people with a previous diagnosis of depression. This held true no matter the person’s age, gender, race or income.
Exercise as a treatment for depression
This chimes with a report published by the American College of Sports Medicine in Indiana, which found that the more exercise people did, the less likely they were to experience depression later in life. For people who did 30 minutes of physical activity every day, the odds of experiencing depression was slashed almost by half. On the flip side, sedentary behaviour seems to raise the risk.
For people who have a current diagnosis of depression, there is also good news. Earlier this year, a meta-analysis study pooling the results from over 41 studies involving more than 2000 adults found that resistance exercise (such as lifting weights) or moderate intensity aerobic exercise, performed with supervision or in a group, was an effective treatment for people with a diagnosis of major depressive disorder or those with symptoms of depression.
Chekroud’s study found that all types of activity were associated with a reduction in poor mental health days. The strongest link was for team sports, followed by cycling, aerobic exercise and gym workouts. But lighter activity like walking or doing household chores counted, reducing the number of poor mental health days by almost 17.7 and 10 per cent, respectively. The benefits were comparable, and often bigger, than other predictors of good mental health, such as a higher level of education or higher household income.
Exercise and mood
Strength training, such as lifting weights or doing push-ups, has also been found to reduce anxiety in adults, help ease symptoms of depression and boost self-esteem – one of the main reasons I chose a chin-up challenge as my New Year goal.
Chekroud’s study wasn’t perfect: it looked at a population at a particular point in time, rather than a trial or intervention. That means we can’t definitively say that exercise caused the effects. Still, the evidence is building that exercise could be an effective way to boost our mood, which is why I now plan workouts into my week as non-negotiable meetings.
It needn’t be a long session. Chekroud’s team found that more exercise didn’t always equate to more of a mood boost. For most kinds of exercise, 30 to 60 minutes per day was the ideal, associated with the lowest mental health burden. The benefits of jogging and cycling, for instance, peaked at 45 minutes.
If you need any more persuasion to plan a lunchtime workout, it also improves your cognitive skills. “I encourage people to exercise earlier in the day, because the afternoon will be more productive. I’m surprised that isn’t happening more,” says Lubans.
Improving children’s behaviour
When it comes to untangling the links between exercise and cognition, most research has focused on childhood and older age as these are the times when the biggest changes in the brain take place – and so also the times when the influence of environmental factors are especially strong.
In childhood, our brains undergo rapid development, building connections that allow us to master new skills. During this window, the brain is particularly sensitive to the impact of movement. Inactivity is associated with worse academic performance in children as well as lower scores on standard cognitive tests.
A small amount of exercise can make a big difference. In 2009, Charles Hillman at Northeastern University in Boston and his colleagues were the first to show that if schoolchildren aged around 9 did a single bout of moderate exercise – walking for just 20 minutes on a treadmill – they saw an almost instant improvement in brain function, cognition and academic performance, scoring better in tests of maths and reading compared with when they sat still. Other research has found that when children aged 8 to 10 took a 15 to 20-minute walk or run before school, they showed better “on-task” behaviours, such as listening or following rules, compared with days when they didn’t walk or run.
Hillman is now looking into the mechanism behind these effects, with the hope of being able to influence policy on the way exercise is incorporated into schools.
The teenage years also seem to be a crucial window for the effects of exercise on the brain. Studies looking at male Swedish teenagers who were conscripted to the army aged 18, and followed up for decades, have found that low fitness at age 18 was associated with an increased risk of serious depression in adulthood, as well as early onset dementia.
Likewise, Lubans’s team found that 8 to 20-minute exercise breaks, three times a week for six months, not only improved teenagers’ fitness, but improved their focus in class. In those with poor mental health, it also reduced perceived stress and lowered feelings of sadness and anxiety.
The cognitive effects of exercise aren’t reserved for children and teenagers. Research has revealed that keeping active can improve all sorts of thinking skills in adults too, including memory, concentration and creativity, supporting the idea that taking a break from work to exercise could make us all more productive.
Exercise to prevent dementia
It could also be one of the best investments for our future. “We’ve seen that exercise could be potentially one of the biggest factors to prevent Alzheimer’s disease and other types of dementia,” says Eef Hogervorst, who studies exercise and cognition at Loughborough University in the UK. And unlike a healthy diet and giving up smoking, which have the biggest impact on the brain if done before you develop dementia symptoms, says Hogervorst, exercise is beneficial until you die.
Compelling evidence that exercise keeps brains youthful comes from a meta-analysis that pooled 15 studies totalling over 30,000 participants, who were followed for up to 12 years. It found that people who exercised – even at low intensity – had an almost 40 per cent lower risk of cognitive decline. Another analysis that included 45 studies that followed 100,000 people for as long as 28 years found that when people did regular moderate or high-intensity exercise, it reduced the risk of developing cognitive problems by 18 per cent.
Hogervorst points out that exercise is one of the few things you can do to not only help prevent dementia, but also to slow down decline if you are already experiencing symptoms. In people with and without dementia, memory improves just 24 hours after a single resistance band session, and the results are even better after several weeks, says Hogervorst.
The evidence isn’t unanimous, however, and in recent months some large reviews of studies have questioned whether such results have been overhyped. There may be many reasons for inconsistent results, says evolutionary biologist David Raichlen at the University of Arizona. The age of participants, the types of exercise performed and the parts of the brain that are targeted will all have an impact. “What the inconsistency really tells us is that there is much more work to do,” he says.
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Conflicting results make it even more important to understand the mechanisms underlying any effects, and this is where things have really taken off lately. One of the most familiar explanations is that “what is good for the body is good for the brain”. The brain is ravenous, burning through a huge amount of energy and requiring a constant supply of oxygen and nutrients to be delivered through the circulatory system. Exercise helps keep this network of blood vessels healthy and blood pressure low. This is important because studies have shown that high blood pressure is linked to a reduction in cognitive performance and is a risk factor for dementia. Exercise also reduces the risk of diabetes and obesity, both strong risk factors for neurodegeneration later in life.
Exercise does more than just pump more blood to the brain, however. It is easy to think of your muscles as passive workhorses that respond to signals from the brain when we need to walk, run or attempt a chin-up. But skeletal muscles – those attached to our bones that we activate when we exercise – are far from passive. They are constantly communicating with the rest of the body, including the brain. When we exercise, our muscles pump out a potent cocktail of hormones and other proteins, many of which can travel to the brain. Called myokines, these are thought to be so influential on our mood and behaviour that they have been nicknamed the “hope chemicals”.
Growing new brain cells
Myokines have also been implicated in the growth of new brain cells. Historically, it was thought that we were born with all the brain cells we will ever have, but we have since discovered that exercise is one of the few things that can spur new brain cell growth.
The most well-studied hope chemical, brain-derived neurotrophic factor (BDNF), has been linked to the growth of new brain cells in the hippocampus of humans, and improvements in learning and memory. A flurry of new cells in the hippocampus could be one explanation for the cognitive boost experienced after exercise. A lack of new cell growth in the brain has also been implicated in dementia and mental health conditions, so encouraging this growth could explain the improvements we see in people affected by these, too.
The more we understand about these chemicals, the more we can try to home in on which kinds of exercise produce them and therefore are the most beneficial, and in what dose. Some answers are starting to emerge. One paper looked at studies of three types of exercise: aerobic exercise, intense anaerobic exercise such as HIIT training, and strength training (hello chin-ups!). For a start, it found that HIIT training seemed to offer more cognitive improvements than lower intensity aerobic exercise. Strikingly, strength training seemed to result in a greater variety of myokines being released from muscles. One of these, insulin growth factor 1, enhances the growth and survival of neurons, and has been linked with cognitive performance. Another, irisin, is often reduced in people with Alzheimer’s disease.
All of this could help explain why older women with mild cognitive impairment who were at risk of developing Alzheimer’s and did resistance training twice a week for six months scored better on tests of attention and memory than those who did aerobic exercise or stretching.
High grip strength, which is a good proxy for overall muscle strength, is associated with better memory and reaction times as well as spatial and verbal cognitive skills in people over 65, and is linked to higher attention and reasoning skills. In fact, the effects of muscle on the mind are so strong that it can even be used as a predictor of cognitive decline: if you lose your grip strength, your cognitive power will probably follow suit. So while aerobic exercise that gets the blood – and all of those vital chemicals – pumping round the body is a good bet, resistance training seems like it could give the most bang for its buck.
Runner’s high
Exercise can also help brain cells communicate more efficiently by directly boosting neurotransmitters, such as GABA and glutamate. While this seems to improve memory, it could also play a role in mood, since low levels of these chemicals are implicated in depression. It has also been shown to boost other neurotransmitters, such as dopamine – leading to the feeling of euphoria or “runner’s high”.
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| Group exercise can combat feelings of loneliness and isolation and protect against various mental health conditions Islandstock/Alamy |
All of these are short-term shifts in brain activity, but both Hillman and Lubans have found evidence that exercise can cause long-term structural and functional changes to the brain, too. Lubans has shown how exercise boosts metabolism in the hippocampus, helping it deliver the ingredients for structural change, and Hillman has demonstrated that exercise helps improve white matter integrity, which helps different parts of the brain speak to one another, allowing people to process information quicker and do better mental gymnastics like multitasking and planning.
When it comes to choosing the best exercise for you, you might want to consider who you do it with. Chekroud and his colleagues found team sports to be the most beneficial for mental health, which makes sense given that social activity promotes resilience to stress and reduces risk of depression. The social side of team sports could also help to reduce the social withdrawal and feelings of isolation that often go hand in hand with depression and other mental health issues.
There is also a school of thought that says the best exercise is one that is cognitively stimulating or, to put it another way, one that makes you move and think at the same time, such as rock climbing, team sports or martial arts. This may have roots in the way our ancestors evolved to be active. When they began walking on two legs and hunting their food over long distances, the simultaneous demands of navigating, communicating and scanning the environment while on the move would have put a huge new cognitive burden on our species. Some researchers believe that this could have been what drove the development of our larger, smarter brains.
This suggests that we may need to challenge our brains to see the biggest benefits, and it may be one explanation for why we sometimes find inconsistent results between individuals and different studies, says Raichlen. Indeed, Tracy Alloway at the University of North Florida and her colleagues found that adults who engaged in cognitively demanding exercises performed better later on in tests of memory compared with those who took yoga classes.
Finally, whatever you choose, make sure it is something you enjoy. Unsurprisingly, studies show that people who are made to do tough levels of exercise in lab experiments experience a dip in their mood. I have come to love my own fitness challenge. My chin-up is still elusive, but it is inching closer. In the meantime, my mental muscle is in better shape than ever.
HACK YOUR EXERCISE FOR THE BEST BRAIN BOOST
1. Pick activities that keep you on your toes and challenge your brain. Think sports like hockey, badminton and football. They lead to a bigger boost of brain-derived neurotrophic factor, or BDNF, a protein that promotes new brain cell growth and its associated cognitive benefits.
2. If you are studying, try learning on the go. In a study of people memorising new Polish vocabulary, participants remembered more new words if they walked while they studied.
3. Struggling to give up smoking? A mere 15 minutes of moderate exercise reduces cigarette cravings – and dampens down activity in brain areas that drive the urge.
4. Exercise that happens as a result of work isn’t as effective as that done by choice, so try to make time for it in your diary, and have fun.
5. Don’t make excuses: even a single bout of exercise is enough to boost executive functions, thinking speed, attention and memory.
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