Stopping exercise for 10 days reduces brain blood flow

Stopping exercise for just 10 days can lead to significant decrease in blood flow to several regions of the brain, including the hippocampus which plays an important role in learning and memory, a new study has found.

The study led by researchers at University of Maryland School of Public Health in the US examined cerebral blood flow in healthy, physically fit older adults (ages 50-80 years) before and after a 10-day period during which they stopped all exercise.

Using Magnetic resonance imaging (MRI)brain imaging techniques, they found a significant decrease in blood flow to several brain regions, including the hippocampus, after they 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, 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," said Smith.

"So, it is significant that people who stopped exercising for only 10 days showed a decrease in brain blood flow in brain regions that are important for maintaining brain health," said Smith.

The participants were all "master athletes," defined as people between the ages of 50 and 80 (average age was 61) who had at least 15 years history of participating in endurance exercise and had recently competed in an endurance event.

Their exercise regimens must have entailed at least four hours of high intensity endurance training each week.

On average, they were running 59 kilometres each week. This group had a maximal oxygen uptake (V02 max) above 90 per cent for their age.

This measure of the maximal rate of oxygen consumption of an individual reflects their aerobic physical fitness.

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

They found that resting cerebral blood flow significantly decreased in eight brain regions, including the 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.

"We know that if you are less physically active, you are more likely to have cognitive problems and dementia as you age," said Smith.

"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," he said.

The study was published in the journal Frontiers in Ageing Neuroscience.