We all know aerobic exercise (e.g. running, swimming, walking briskly) is good for the heart, and apparently it's also good for the brain. Of course, if one neglects to keep up with the activity, fitness declines. Dr. J. Carson Smith from the University of Maryland in College Park and colleagues wanted to know what happens to the brains of older folks who exercised vigorously and often if they stopped exercising. The report of their study was published in the journal Frontiers in Aging Neuroscience. In particular, they investigated what would happen to the blood flow to two parts of the brain — the overall cerebrum (controls voluntary actions, emotions, etc.) and the hippocampus (area under cerebral cortex important for learning and memory).
They recruited 9 adults (7 men, 2 women) -- master athletes from local running clubs — older than 50 years (age range was 50-80) who had been involved in endurance exercise for at least 15 years, and who had competed in endurance exercise events. On average they had participated in continuous endurance training for about 29 years (range 20-36 years), were running an average of 36 miles per week, and exercising 5 days per week. These participants were requested to cease training and abstain from any vigorous exercise for 10 days. Before and at the end of the 10 days blood flow to the cerebrum and hippocampus was measured by MRI (Magnetic Resonance Imaging).
Analysis of the MRI data indicated that the 10-day exercise abstention resulted in significant reductions in cerebral blood flow in eight individual regions. Similarly, blood flow to the hippocampus region was also significantly reduced at the end of the 10-day abstention.
Thus, not only does exercise abstention in physically fit individuals decrease physical fitness, it seems to have a potentially important affect on the brain. While it is true that the investigators did not find any effects on cognitive function, which they assessed with a verbal fluency test, obviously one implication of this study is the positive effect that regular exercise might have on brain function.
These results must be replicated in larger sets of individuals — and in less fit people before we can assume the results can be generalized to others. Further, as the authors pointed out, we don't know if resumption of their exercise habits would have restored the previous level of blood flow to these brain regions.
At a time when a large segment of the population is aging and concerns are widespread about loss of cognitive function, it is imperative to understand any factors which might be involved in maintaining or improving functionality of the aging brain.