Exercise helps brain function. As long as you continue exercising blood flow improves and the metabolites gain entrance into the brain. The brain is engaging in what it likes best; action.
But when the exercising stops so does brain health.
To expound on this idea is an article written by published by New York Times where you can read more in detail.
Improvements in brain reduce when exercise stops
Exercise prompts these changes in large part by increasing blood flow to the brain, many exercise scientists believe. Blood carries fuel and oxygen to brain cells, along with other substances that help to jump-start desirable biochemical processes there, so more blood circulating in the brain is generally a good thing.
Exercise is particularly important for brain health because it appears to ramp up blood flow through the skull not only during the actual activity, but throughout the rest of the day. In past neurological studies, when sedentary people began an exercise program, they soon developed augmented blood flow to their brains, even when they were resting and not running or otherwise moving.
But whether those improvements in blood flow are permanent or how long they might last was not clear.
So for the new study, which was published in August in Frontiers in Aging Neuroscience, researchers from the department of kinesiology at the University of Maryland in College Park decided to ask a group of exceedingly fit older men and women to stop exercising for awhile.
“We wanted to study longtime, serious endurance athletes because they would be expected to have a very high baseline” level of aerobic fitness and established habits of frequent exercise, says J. Carson Smith, an associate professor of kinesiology at the University of Maryland and senior author of the study. If these people abruptly stopped exercising, he says, the impacts could be expected to be more outsized than among people who worked out only lightly.
The researchers eventually found 12 competitive masters runners between the ages of 50 and 80 who agreed to join the study. All had been running and racing for at least 15 years and still regularly ran 35 miles a week or more.
At the start of the experiment, the runners visited the researchers’ lab for tests of their cognitive skills. They also had a special brain M.R.I. that tracks how much blood is flowing to various parts of the brain.
The researchers were particularly interested in blood flow to the hippocampus, a portion of the brain that is essential for memory function.
Then the athletes sat around for 10 days. They did not run or otherwise exercise and were asked to engage in as little physical activity as possible.
While some people might find such a directive easy to follow, these men and women loved to work out, Dr. Smith says, and might have been tempted to cheat and jog just a little. But researchers “called them frequently,” he says, to gently remind them to remain couch-bound.
After 10 days of being sedentary, the erstwhile runners returned to the lab to repeat the earlier tests, including the M.R.I. scan of their brains.
The results showed striking changes in blood flow now. Much less blood streamed to most of the areas in the runners’ brains, and the flow declined significantly to both the left and right lobes of the hippocampus.
Encouragingly, the volunteers did not perform noticeably worse now on the tests of cognitive function than they had at the start.
But the results do suggest that the improvements in brain blood flow because of exercise will diminish if you stop training, Dr. Smith says.