Five Different Physical Exercises That Affect The Brain In Very Different Ways
Pumping iron to sculpt your biceps. Yoga poses to stretch and relax. Running to whittle your waistline and get fit fast. There are loads of reasons why it's smart to exercise, and most of us are familiar with the menu of options and how each can shape and benefit your body. But we are discovering that there are numerous ways in which exercise makes you smart too. Many of its effects have been going unnoticed, but if you were to peer inside the heads of people who like to keep active, you'd see that different exercises strengthen, sculpt and shape the brain in myriad ways.
But a new chapter is beginning in our understanding of the influence of physical exercise on cognition. Researchers are starting to find more specific effects related to different kinds of exercise.
Specifically, high-intensity intervals, aerobic exercise, weight training, yoga and sports drills are affect different areas of the brain.
They are looking beyond the standard recommendation of 30 minutes of moderate, aerobic exercise a day, for the sake of your brain. Are there benefits to going slower or faster? To lifting weights, or performing sun salutations? Whether you want a boost in focus for an exam, find it hard to relax or are keen to quit smoking, there's a prescription for you.
"Lifting weights helps improve complex thoughts, problem-solving and multitasking"
The first clue that exercise affects the brain came from rodent studies 15 years ago, which showed that allowing mice access to a running wheel led to a boost in neuron formation in their hippocampi, areas of the brain essential for memory. That's because exercise causes hippocampal neurons to pump out a protein called brain-derived neurotrophic factor (BDNF), which promotes the growth of new neurons. The mice showed improvements in memory that allowed them to navigate mazes better.
The findings were soon translated to humans. Older adults who did aerobic exercise three times a week for a year also grew larger hippocampi and performed better in memory tests. Those with the highest levels of BDNF in their blood had the biggest increases in this brain region.
The idea that exercise helps to improve memory has been especially welcome given that the search for effective treatments for cognitive decline has been slow in progress. And it now seems that aerobic exercise such as running and cycling may help stave off Alzheimer's disease and other forms of dementia.
As the evidence for aerobic exercise accumulated, Teresa Liu-Ambrose at the University of British Columbia in Vancouver, Canada, began to wonder about other types of exercise. She has been looking for ways to halt dementia in people with mild cognitive impairment (MCI), a population of adults known to be at increased risk of developing dementia, and was especially interested in strength training, which has in recent years been added to US and UK government recommendations for physical activity.
To test the idea, Liu-Ambrose compared the effects of aerobic exercise and strength training in 86 women with MCI. She measured their impact on two abilities known to decline as the condition progresses: memory and executive function -- which encompasses complex thought processes, including reasoning, planning, problem-solving and multitasking.
Twice a week for an hour, one group lifted weights, while the other went for brisk walks quick enough that talking required effort. A control group just stretched for an hour instead. After six months of this, both walking and lifting weights had a positive effect on spatial memory -- the ability to remember one's surroundings and sense of place.
On top of that, each exercise had unique benefits. The group that lifted weights saw significant improvements to executive function. They also performed better in tests of associative memory, which is used for things like linking someone's name to their face. The aerobic-exercise group saw improvements to verbal memory -- the ability to remember that word you had on the tip of your tongue. Simply stretching had no effect on either memory or executive function.
If aerobic exercise and strength training have distinct benefits, is combining them the way to go? To address this, Willem Bossers of the University of Groningen in the Netherlands split 109 people with dementia into three groups. One group walked briskly four times a week for 30 minutes; a combination group walked twice a week and strength-trained twice a week for 30 minutes each; and a control group did no exercise. After nine weeks, Bossers put the participants through a battery of executive-function tests that measured problem-solving, inhibition and processing speed. He found that the combination group showed more improvement in executive function than the aerobic-only or control groups. "It seems that, for older adults, walking only is not enough. They need to do some strength training," he says.
Immediate Attention Boost
And these benefits extend to healthy adults too. In a year-long trial of healthy older women, Liu-Ambrose found that lifting weights, even just once a week, resulted in significant improvements in tests of executive function. Balancing and toning exercises, on the other hand, did not.
The combination of lifting weights and aerobic exercise might be particularly powerful because strength training triggers the release of a molecule called insulin-like growth factor-1 (IGF-1), a growth hormone produced in the liver that is known to affect communication between brain cells, and to promote the growth of new neurons and blood vessels. On the other hand, aerobic exercise mainly boosts BDNF, says Liu-Ambrose. In addition, Bossers says strength training also decreases levels of homocysteine, an inflammatory molecule that is increased in the brains of older adults with dementia. By combining aerobic exercise with strength training, you're getting a more potent neurobiological cocktail. "You're attacking the system in two ways," he says.
Another approach is to start young, with findings that different types of exercise affect a child's mental capacity in a number of ways. For example, if you want kids to focus for an hour -- on a maths test, say -- the best bet is to let them have a quick run around first. That's according to studies that show a simple 20-minute walk has immediate effects on children's attention, executive function and achievement in mathematics and reading tests. Letting kids sprint or skip about has the same effect. A brisk walk can also help children with attention-deficit hyperactivity disorder to focus, although again it's not yet clear how long the effects last.
These findings should be used to make decisions about the daily school routine, says Charles Hillman at the University of Illinois at Urbana-Champaign, who carried out some of the research. He agrees with current recommendations that children get at least an hour of exercise daily, but notes that it might be best spread over the course of the day. Because purely aerobic exercise keeps kids focused in the near term, giving them breaks to walk or move around every 2 hours might be the best way to promote learning.
In contrast, exercise that is highly structured and focused on specific skills, such as for a sport or to improve coordination, hampers attention. A bunch of drills and rules may be too taxing for children right before a test or a situation that requires sustained focus.
Instead, these kinds of specific exercises seem to build up attention span gradually over the long-term. In research yet to be published, Maria Chiara Gallotta at the University of Rome in Italy found that twice-weekly sessions of coordinative exercises, such as basketball, volleyball or gymnastics practice, over the course of five months helped children do better on tests that required concentration and ignoring distractions.
The cerebellum -- the finely wrinkled structure at the base of the brain -- has been long known to be involved in coordinating movement, but is now recognised as having a role in attention as well. Practising complicated movements activates the cerebellum and, by working together with the frontal lobe, might improve attention in the process.
Making sure children are physically fit can have lasting cognitive benefits too, says Hillman. He has shown that children who are fit have larger hippocampi and basal ganglia, and that they perform better in attention tests. The basal ganglia are a group of structures important for movement and goal-directed behaviour -- turning thoughts into actions. They interact with the prefrontal cortex to influence attention, inhibition and executive control, helping people to switch between two tasks, such as going from sorting cards by colour to sorting cards by suit.
Hillman focuses on children aged 8 to 11 because areas like the hippocampi and basal ganglia are still maturing, so intervening at a young age can make a big difference. And even small gains in fitness lead to measurable changes in the brain. In some of his studies, Hillman has put kids on year-long after-school fitness programmes. Many are overweight, and while they don't lose much weight, their brains do change. They're going from being unfit to slightly less unfit, says Hillman. "But we're still finding benefits to brain function and cognition."
Voelcker-Rehage found that these types of exercise improved visual-spatial processing, required for mentally approximating distances -- for instance, being able to assess whether you have time to cross the street before an oncoming car reaches you -- more than aerobic exercise.
Another explanation comes from recent research by Tracy and Ross Alloway, both at the University of North Florida in Jacksonville. They found that just a couple of hours of activity of the type we often enjoy during childhood, such as climbing trees, crawling along a beam, or running barefoot, had a dramatic effect on working memory.
This is the ability to hold on to information and manipulate it in our minds at the same time. "It prioritises and processes information, allowing us to ignore what is irrelevant and work with what is important," says Tracy Alloway. "Working memory influences nearly everything that you do, from the classroom to the boardroom."
So what is it about climbing trees or beam balancing that is so beneficial? The researchers only found positive results when the activities were a combination of two things. They needed to challenge the sense of proprioception -- the position and orientation of the body -- and also needed at least one other element, such as navigation, calculation or locomotion. Basically, the advantages came from exercises in which we need to balance and think at the same time.
The more we learn about the effects of exercise on the brain, the more different types of benefits are emerging, extending beyond cognition to changes in behaviour.
One of the most popular fitness trends of the last few years is high-intensity interval training, which involves quick spurts of all-out exercise. Its sheer toughness is claimed to provide the same benefits as longer efforts in a fraction of the time.
These workouts might have an extra advantage: short bursts of activity can help curb cravings. And although the tougher the better, they don't necessarily have to be gut-bustingly hard.
To test the effects of intensity training on appetites, Kym Guelfi at the University of Western Australia in Perth invited overweight men to come into the lab on four separate occasions. On three of the visits, they spent 30 minutes on an exercise bike, but at different intensities -- a moderate, continuous pace; alternating between intervals of high-intensity cycling for 1 minute followed by 4 minutes of moderate cycling; or alternating between very high intensity, 15-second sprints followed by one really easy minute. The fourth visit consisted of resting for the full 30 minutes.
After the most intense intervals, the men ate less of the provided, post-workout porridge and less food overall for the next day and a half compared with days they cycled moderately or simply rested.
One explanation could be that the exercise reduced levels of the "hunger hormone", ghrelin. This is responsible for telling the part of the brain that controls eating -- the hypothalamus -- when the stomach is empty. When full, ghrelin production shuts off and hunger wanes. Following the most intense intervals of exercise, ghrelin levels were lowest.
What is clear is that these effects can endure well into old age, and it's never too late to start. The hippocampus shrinks as we get older, leading to the typical struggles with memory. But aerobic exercise not only prevents this loss -- it reverses it, slowing the effects of getting older. Voelcker-Rehage has found that the brain requires less energy to complete certain tasks after exercise. "We would say that points to the fact that the brain is more efficient," she says. "It works more like a young brain."
And in a study looking at yogis that had been practising for many years, Sara Lazar at Massachusetts General Hospital found that some brain regions were remarkably well preserved compared with those of healthy controls that were matched for age, gender, education and race. "The 50-year-old's brain looked like a 25-year-old's," notes Lazar.
If you're still unsure which type of exercise to pick, there's some overlap between the different exercises and benefits, so Liu-Ambrose's suggestion is simple: "If you're not active, do something that you enjoy." The best exercise is the kind that you'll actually do.