In their study paper, the researchers discuss how evidence shows endurance exercise training improves cerebrovascular health and has positive effects on the hippocampus, but what happens to these benefits if exercise ceases is somewhat unclear. Significant reductions in brain blood flow 
 
 Using magnetic resonance imaging (MRI) brain scans, the team measured brain blood flow in healthy, physically fit older adults aged from 50-89 years (average 61) before and after a 10-day period during which they stopped all 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. From the brain scans, the researchers were able to assess the velocity of blood flow while the participants were at peak fitness and then again after 10 days of no exercise. 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. Our participants had a mean continuous endurance training history of ~29 years, and on average were running 59 km per week and training 5 days per week just prior to the baseline testing. However, the researchers found no significant change in cognitive function - measured using verbal fluency tests - in the participants from before to after they stopped exercising.
– Think it's OK to take a week off from working out? Think again ... if you even can. A study published last month in Frontiers in Aging Neuroscience finds the benefits of exercise on the brain can fade after just 10 days. Previous studies have shown that exercise increases blood flow to the brain, which can create new neurons, increase volume in important places, and possibly even improve memory and thought, the New York Times reports. But it was unclear how long that healthy increased blood flow and its benefits would last. Now we know: Less than 10 days. Researchers looked at a dozen "exceedingly fit" seniors—ages 50 to 80—who still ran 35 or more miles per week. After 10 days of doing nothing, the seniors had less blood flow to eight regions of their brain, including significantly less to the hippocampus, which is associated with memory, Medical News Today reports. Medical Daily quotes the study's lead author, Dr. J. Carson Smith, who says the hippocampus is "one of the first brain regions to shrink in people with Alzheimer's disease." The seniors didn't perform any worse on cognitive tests after 10 days of loafing about, and more research is needed to see if a cessation of exercise actually impacts the functioning of the brain. In the meantime, keep on that workout schedule. (Eleven hours of this brain game can cut dementia risk in half.)