We all know regular exercise comes with numerous brain health benefits, like improving memory and thinking skills, helping to ward away cognitive decline in old age. However, hitting pause on our workout routine could weigh heavy on our conscious — literally. A recent study published in the journal Frontiers in Aging Neuroscience found stopping exercise for just 10 days can significantly reduce blood flow to several brain regions, including the hippocampus.

"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, lead author of the study and associate professor of kinesiology at University of Maryland School of Public Health (UMD), in a statement.

Typically, the hippocampus shrinks in late adulthood, which is what leads to impaired memory and increased risk for dementia. Previous research has found the hippocampus responds to exercise training by increasing in volume, and leading to improvements in spatial memory. Aerobic exercise training can be effective at reversing hippocampal volume loss in late adulthood, which is accompanied by improved memory function.

In the UMD study Smith and his colleagues observed ‘master athletes” who were between the ages of 50 and 80 (average age was 61), who had at least 15 years history of participating in endurance exercise, and who have recently competed in an endurance event. The participants' exercise routines included at least four hours of high intensity endurance training each week. On average, they were running ~36 miles each week or the equivalent of a 10K run a day. This group also had a VO2 max — the maximum amount of oxygen the body is capable to use of in one minute — above 90 percent for their age.

An MRI scan was used to measure the velocity of blood flow in the brain while the athletes were following their regular training routine, specifically at peak fitness, and again after 10 days of no exercise. The researchers noted resting cerebral blood flow significantly decreased in eight brain regions, including the areas of the left and right hippocampus, and other regions known to be part of the brain's "default mode network" — a neural network known to deteriorate quickly with Alzheimer's disease. It's important to note these significant changes were regionally specific.

“[T]he take home message is simple - if you do stop exercising for 10 days, just as you will quickly lose your cardiovascular fitness, you will also experience a decrease in blood brain flow” said Smith, about the findings.

A similar study published in the journal Neurology found less fit middle-aged adults saw loss of brain volume after 20 years. Participants performed treadmill tests to estimate their “exercise capacity,” which was measured by monitoring the amount of time they could exercise before their heart rate passed a threshold. The researchers found for every The researchers found those who saw their blood pressure and heart rate surge the most during the treadmill test were “more likely to have smaller brain volumes two decades later,” they wrote. In other words, there was a direct correlation between poor fitness levels and brain volume decades later, which indicates accelerated brain aging.

Stopping exercise for awhile, or the lack of exercise, has important implications on our brain health. More research is needed to confirm how fast these changes occur, and what the long term effects could be. Researchers will also need to look into if these brain changes could be reversed with the resumption of exercise.

Source: Alfini AJ, Weiss LR, Leitner BP et al. Hippocampal and Cerebral Blood Flow after Exercise Cessation in Master Athletes. Front. Aging Neurosci. 2016.

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