The researchers found significant reductions in resting brain blood flow in eight brain regions in fit older adults who stopped exercising.
This was the key finding of a new study - led by the University of Maryland (UMD) School of Public Health and recently published in the journal Frontiers in Aging Neuroscience - that adds to growing evidence of links between physical fitness and cognitive health.
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.
Lead author J. Carson Smith, associate professor of kinesiology at UMD says we know that the hippocampus is important for learning and memory.
He explains that studies of mice and rats have shown exercise increases growth of new blood vessels and brain cells. Also, research shows that in older people, exercise can protect the hippocampus from shrinking. He notes:
"So, it is significant that people who stopped exercising for only 10 days showed a decrease in blood flow to brain regions that are important for maintaining cognitive health."
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.
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.
The results showed significant reductions in resting brain blood flow in eight brain regions - including the right and left hippocampus.
The other regions included parts of the "default mode network" - a brain structure that is known to deteriorate quickly in people with Alzheimer's disease.
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.
The participants who volunteered for the study were all "master athletes" whom the researchers describe as "a unique population and should not be considered equivalent to older adults who engage in regular moderate to vigorous intensity leisure-time physical activity."
The researchers were not surprised to find these senior athletes scored high for their age on aerobic fitness. Their VO2 max was in the top 10 percent for their age group (above the 90th percentile). VO2 max is the volume of oxygen a person consumes while exercising at their maximum capacity.
With an average continuous endurance training history of around 29 years, the volunteers regularly took part in national and regional events.
Just before taking part in the study, they were running an average of 59 kilometers a week and training on 5 days a week.
"We know that if you are less physically active, you are more likely to have cognitive problems and dementia as you age. However, we did not find any evidence that cognitive abilities worsened after stopping exercising for just 10 days. But the 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."
Prof. J. Carson Smith
The researchers say their findings point to a need for further research to discover how fast the brain blood flow changes occur, what their long-term effects could be, and whether they can be reversed by taking up exercise again.