If you’ve ever had to stop working out — due to injury, illness, travel or from just being too busy — you know how quickly you can lose muscle. But have you ever thought something similar could happen to your brain?

Researchers at the University of Maryland School of Public Health examined cerebral blood flow in healthy, physically fit older adults (ages 50 to 80 years) before and after a 10-day period during which they stopped all exercise. The findings may surprise you.

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Using MRI brain imaging techniques, the researchers found a significant decrease in blood flow to several brain regions, including the hippocampus, after people stopped their exercise routines.

“We know that the hippocampus plays an important role in learning and memory and is one of the first brain regions to shrink in people with Alzheimer’s disease,” said Dr. J. Carson Smith, associate professor of kinesiology and lead author of the study.

“In rodents, the hippocampus responds to exercise training by increasing the growth of new blood vessels and new neurons, and in older people, exercise can help protect the hippocampus from shrinking. So it is significant that people who stopped exercising for only 10 days showed a decrease in brain blood flow in regions that are important for maintaining brain health.”

Many studies have documented what detraining or stopping an exercise program will do to the metabolic system, Smith told LifeZette. People lose muscle, flexibility, and coordination. They gain weight and often see a rise in blood pressure — even become diabetic.

This is the first study to have looked at brain detraining, he believes.

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The catch here is that all of the study participants were “master athletes,” meaning they were between the ages of 50 and 80 (average age was 61) with at least 15 years experience in endurance exercise and competition. Their exercise regimens entailed at least four hours of high-intensity endurance training each week.

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On average, they were running about 36 miles each week — or the equivalent of a 10K run a day.

Researchers measured the velocity of blood flow in the brain with an MRI scan while the individuals were still following their regular training routine (at peak fitness) and again after 10 days of no exercise.

Resting cerebral blood flow significantly decreased in eight brain regions, including the areas of the left and right hippocampus and several regions known to be part of the brain’s “default mode network” — a neural network known to deteriorate quickly with a diagnosis of Alzheimer’s disease.

“I was surprised at how many of these regions were significant,” said Smith. “I wasn’t expecting we would have as many. It’s also somewhat alarming and at the same time encouraging that exercise, when you are training — you are affecting those brain regions in a positive manner.”

The information adds to the growing scientific understanding of the impact of physical activity on cognitive health. The less physically active you are, the more likely you are to have cognitive problems and dementia as you age.

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The take-home message is simple, said Smith, even for armchair athletes: If you stop exercising for even 10 days, just as you will quickly lose your cardiovascular fitness — you will also experience a decrease in blood brain flow.

“Keep going. Stay with your exercise program as best as you can. Obviously, everybody has their hiccups and we know that most of the population struggles to be active. [With] this kind of study, I try to point out and I hope motivate people to be more physically active and maintain those levels.”

Smith believes this could have important implications for brain health in older adults. He points to the need for more research to understand how fast these changes occur, what the long-term effects could be, and how fast they could be reversed when exercise is resumed. The findings were published in Frontiers in Aging Neuroscience in August 2016.