How Exercise May Help Clean the Brain

We know physical exercise supports our physical health, but growing research shows that it may also improve brain health. A recent study published in Nature Neuroscience, for instance, found that even simple bodily movements - such as tensing the abdominal muscles - may trigger a process that helps clear waste from the brain.

But how does this actually happen, and what does it mean to “clean” the brain? We spoke with neurology experts to find out, as well as to explore other ways exercise may support brain health.

How does exercise “clean” the brain?

The study found that when we move our bodies, even in subtle ways, the abdominal muscles create pressure changes that gently shift the brain within the skull. “This matters because movement appears to aid the circulation of cerebrospinal fluid, the fluid surrounding the brain and spinal cord,” says David Perlmutter, a board-certified neurologist and author of Brain Defenders: Harness the Power of Your Immune Cells to Protect Your Brain for Life. “Researchers believe this effect on cerebrospinal fluid may help the brain clear waste that could otherwise contribute to neurodegenerative diseases.”

So far, this research has only been conducted in mice, meaning its findings cannot yet be directly applied to people. However, “basic scientific research like this is how we build the foundation for understanding human biology,” says Janina Kamm, PsyD, a clinical neuropsychologist and assistant professor at The Chicago School.

Before we can fully understand how to keep the human brain healthy, we first need to understand the mechanics behind how it works. Studies such as this one help researchers develop that knowledge, according to Kamm. “While the exact ‘how’ and ‘why’ are still being uncovered, the scientific evidence for the benefits of physical exercise in humans is already enormous,” she says. “Of all the things we can do to promote a healthy brain, regular physical activity is among those supported by the most robust evidence.”

Brain movement and fluid circulation

The study’s findings are of interest to researchers because when the brain moves within the skull, the fluid inside and around it moves too, Kamm explains. “There is another fluid called interstitial fluid, which sits between brain cells and carries away the waste produced by the brain,” she says. “In theory, movement of the brain could push interstitial fluid outwards, towards the space around the brain, where we have an innate drainage system. By encouraging this fluid to move towards our waste-removal systems, we may be able to ‘clean’ the brain more effectively.”

What does it mean to “clean” the brain?

So, what exactly do we mean when we talk about “cleaning” the brain? It does not involve soap and water, but the underlying idea is similar.

“Brain ‘washing’ or ‘cleaning’ refers to the biological process in which fluid flows into, through and out of brain tissue to remove metabolic waste,” says D. Kojo Hamilton, MD, a board-certified spinal neurosurgeon and professor of neurosurgery at the University of Pittsburgh School of Medicine.

Two primary fluids carry out this work: cerebrospinal fluid (CSF) - the clear fluid surrounding the brain - and interstitial fluid (ISF), which is found in the spaces between brain cells. These fluids travel through and around brain tissue, helping to remove metabolic waste, inflammatory compounds, excess proteins and cellular debris, Dr Perlmutter explains. “One simple way to think about it is like rinsing a sponge,” he says. “When the brain shifts slightly, fluid moves through the brain tissue and may help clear away unwanted waste.”

Deep sleep, exercise and brain waste removal

We already know that deep sleep plays a vital role in this cleansing process. Earlier research has shown that cerebrospinal fluid flow increases during deep sleep.¹ It rises and helps remove metabolic waste from the brain, including proteins linked to Alzheimer’s disease,² says Dr Perlmutter.

“What makes this new study particularly important is that it suggests we may now have another potential tool to support this ‘cleaning’ process: movement and exercise,” he explains. “The findings indicate that physical activity may encourage fluid movement in the awake brain through gentle mechanical movement of the brain itself.”

This remains an active area of research. “Scientists are still trying to understand the full picture of what happens when this waste-removal system is disrupted or becomes inefficient,” Kamm says.