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If exercise were a drug, we would say its benefits were too good to be true. Not only does it keep us healthy and help us live longer, it makes us smarter and happier, too. Working out can enhance memory, speed up reaction times, improve attention, and alleviate depression. It may even stave off neurodegenerative disorders like Alzheimer’s and Parkinson’s disease.
How does it do all that?
Over the past decade, scientists have started to uncover the ways exercise impacts our brains. Working out increases levels of important hormones and neurochemicals that help forge new connections between brain cells, and may even lead to the birth of neurons in an area of the brain called the hippocampus, the organ’s mood and memory hub.
“Exercise seems to be good for practically every function in the brain and body,” says Fernando Gomez-Pinilla, a professor in the Department of Integrative Biology and Physiology at UCLA.
Every time you work out, your muscles, fat cells, and liver release a variety of molecules into the bloodstream. Some of these molecules circulate through the body and travel up to the brain, where they cross the blood-brain barrier. Once inside, they trigger a cascade of beneficial changes that can make you feel sharper and happier.
One of the most crucial changes is the release of a growth hormone called brain-derived neurotrophic factor, or BDNF. When it comes to exercise’s positive effects on the brain, BDNF is the star.
“Exercise seems to be good for practically every function in the brain and body.”
“This is one of the most important molecules for brain function in connection to the effects of exercise,” says Gomez-Pinilla. “BDNF is very important for all of the basic processes related to learning and memory in the brain.”
BDNF helps the brain build new connections, or synapses, between neurons — a process called synaptic plasticity that is thought to be the foundation for learning. Cells communicate through these connections both within and across areas of the brain. For example, neurons in the hippocampus create synapses with cells in the prefrontal cortex, another region that significantly benefits from exercise. The prefrontal cortex is where a lot of our higher-level executive functions originate, like decision-making and attention, processes that are also improved with exercise.
BDNF’s most remarkable effect is also its most contentious. Years of research show that, at least in rats and mice, exercise-induced BDNF triggers the growth of new brain cells in the hippocampus, a process called neurogenesis. BDNF does this by boosting the function of stem cells in the brain, eventually filling the hippocampus with new healthy cells that enhance brain power.
Whether neurogenesis also happens in adult humans is more controversial. Some studies suggest yes, others no. That’s because there’s no clear way to measure the birth of a new brain cell without cutting open someone’s skull.
“Until there are better, more sophisticated methods that directly address whether neurogenesis is increased by exercise in humans, that remains unclear,” says Henriette van Praag, an associate professor of biomedical science at Florida Atlantic University.
Exercise also changes the brain’s network of blood vessels. More blood flow in the body from exercise corresponds to more blood flow in the brain, as well as the rise of a blood vessel-specific molecule called vascular endothelial growth factor (VEGF). As a result, new blood vessels form in the hippocampus. In rodent brains, neurogenesis and blood flow are connected, potentially because the new blood vessels bring more growth factors to the area. Humans experience the same increase in blood vessels, providing another clue that neurogenesis may be occurring in people.
Anyone who’s felt a “runner’s high” — or just felt less crappy after a workout — has experienced the way exercise elevates neurotransmitters like serotonin, dopamine, and endogenous opioids (also known as endorphins), which are critical for regulating mood, motivation, and feelings of reward. Researchers are less clear about how these changes start — although, like everything else, they appear to be connected to BDNF. It’s possible that these neurochemicals go up simply because exercise is rewarding. Anything that makes you feel good will raise your dopamine levels, for example, so if going to a SoulCycle class is fun for you, your brain will release the reinforcing chemical in response.
So what type of exercise is best for your brain? Most of the research has been done on moderate aerobic exercise like jogging, but recent evidence suggests that weight lifting and high-intensity interval training are good for you, too. Julia Basso, a senior research associate in the Department of Human Nutrition, Foods, and Exercise at Virginia Tech, says people who experience the biggest gains in their fitness show the biggest cognitive changes, suggesting higher-intensity workouts provide extra benefit. However, the mood boosts occur no matter the intensity of the activity.
“You could go for a walk and your mood is going to be lifted up. But you need higher intensity to get cognitive improvements,” Basso says. “The more you’re getting your heart rate up higher and higher, the longer-term fitness benefits you’re going to have, and then the longer-term cognitive benefits.”
If you’re just getting started, though, or you’re limited by age or injury, even walking can bring about some of these changes. The most important thing is to find something that you like doing and will stick with.
“In practical terms,” Basso says, “the best exercise regimen is going to be one that you’re enjoying and that can get you to go back the next day.”