The connection between physical activity and brain health is getting stronger, but we’re still trying to understand all of the reasons why. A new study approached the question with a bit of a twist – by investigating what happens in the brain when leg movement is restricted.
We already know that people unable to move their legs, like patients who are bedridden, lose muscle and bone mass. But scientists have questioned whether the effects run deeper, influencing not only the muscular and skeletal systems but also the brain and nervous system.
To test the question, researchers restricted leg movement in a group of mice for 28 days. Their front legs were free, but their hind legs were immobilized. Another group of mice were free to move around as usual. The brains of both groups were examined at the end of the study period – particularly a brain region called the subventricular zone, a hub of central nervous system activity in vertebrates like mice (and humans).
The study showed that restricting leg movement in the mice resulted in reducing the number of neural stem cells in their brains by 70%, compared to the freely moving control group. This is crucial because neural stem cells are the basis for new cell development via the process known as “neurogenesis.” Without neural stem cells, new neuron growth to replace dying neurons can’t happen and brain health declines. The brains of the immobilized mice also had deteriorated glial cells, which serve the role of protecting and insulating neurons.
The results suggest that leg movement sends signals to the brain that trigger new cell growth and maintain the health of existing cells.
"Neurological health is not a one-way street with the brain telling the muscles 'lift,' 'walk,' and so on,” said lead study author Raffaella Adami of the Università degli Studi di Milano in Italy. "It is no accident that we are meant to be active: to walk, run, crouch to sit, and use our leg muscles to lift things.”
Since this was a mouse study, the results accompany a dose of caution about immediately drawing conclusions for humans. The extent to which new neurons develop in the human brain throughout adulthood is still a topic of debate. But much of the underlying biology in this case applies to both mice and humans, so there’s reason to believe a comparable dynamic plays out in our brains.
“Our study supports the notion that people who are unable to do load-bearing exercises — such as patients who are bedridden, or even astronauts on extended travel — not only lose muscle mass, but their body chemistry is altered at the cellular level and even their nervous system is adversely impacted," said Adami.
The takeaway is yet another reason to stay active, not only for cardiovascular and muscle fitness, but also for the health of our central control system that keeps everything else running.
The study was published in the journal Frontiers in Neuroscience.
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