It is known that exercise benefits the brain, bulking up the size of the hippocampus and improving cognitive function, learning and memory. It is also known what skipping exercise can do to our bodies (not just flabbiness,  but decreasing bone density, muscle quality, and metabolic dysfunction), but it was unknown what the effect of stopping exercise was on the brain.

A team of researchers from the University of Maryland, decided to find out. In the small study, 12 long-term exercisers were asked to quit working out completely for 10 consecutive days. During that time they moved as little as possible.

The participants' brains were scanned before and after and they completed cognitive tests.

In less than two weeks the scans revealed there was significantly less blood flow to the brain, particularly the hippocampus.

"Our participants, however, did not show any changes in cognitive function over the 10-day cessation of exercise period," the paper's authors said, noting that more research was needed to establish whether more extended periods off exercise made a difference.

"I would not want someone to think that if they are on deadline or on vacation for a week or so and don't manage to work out," that the brain is being starved of blood, lead author Dr Carson Smith told theNew York Times.

Nevertheless, Dr Smith wrote in the study paper, their research may provide a useful starting point to explore the long-term effects of inactivity on the brain.

"Just as the effects of long-term endurance exercise training on cardiovascular and metabolic function wane considerably after a short period of detraining, so also may hippocampal and grey matter rCBF [regional cerebral blood flow] be sensitive to exercise cessation," Smith said.

It is important to consider, especially since we often think about how our brain can affect our body, but far less about how our body can affect and change our brain.

"The brain is always embodied, and our subjective experience always has a bodily component, just as all so-called bodily experiences have a mental component," Dr Norman Doidge explained in The Brain's Way of Healing.

The way and intensity with which we move, for instance, stimulates the brain in different ways.

"The data is overwhelming that exercise does at least two things to the brain," Doidge told Fairfax earlier this year.

"One, that it triggers these growth factors that are kind of like fertiliser for the brain cells to enhance connections between them – one of them called Brain Derived Neurotrophic Factor (BDNF), another is glial derived neurotrophic factor, which supports the infrastructure of the brain cells and that enhances health."

Dr Doidge added that various studies show that regular exercise is the most powerful contributor to decreased risk of both general cognitive decline and dementia.

"Our bodies evolved long before brains did," Dr Doidge said, "and they evolved to help bodies coordinate and move ... And it turns out one of the best things you can do for your brain is exercise your body." 

smh.com.au