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Phys Ed Gretchen Reynolds on the science of fitness.

Fitness Tracker Marathon, half-marathon, 10K and 5K training plans to get you race ready.

Two new experiments, one involving people and the other animals, suggest that regular exercise can substantially improve memory, although different types of exercise seem to affect the brain quite differently. The news may offer consolation for the growing numbers of us who are entering age groups most at risk for cognitive decline.

It was back in the 1990s that scientists at the Salk Institute for Biological Studies in La Jolla, Calif., first discovered that exercise bulks up the brain. In groundbreaking experiments, they showed that mice given access to running wheels produced far more cells in an area of the brain controlling memory creation than animals that didn’t run. The exercised animals then performed better on memory tests than their sedentary labmates.

Since then, scientists have been working to understand precisely how, at a molecular level, exercise improves memory, as well as whether all types of exercise, including weight training, are beneficial.

The new studies provide some additional and inspiring clarity on those issues, as well as, incidentally, on how you can get lab rats to weight train.

For the human study, published in The Journal of Aging Research, scientists at the University of British Columbia recruited dozens of women ages 70 to 80 who had been found to have mild cognitive impairment, a condition that makes a person’s memory and thinking more muddled than would be expected at a given age.

Mild cognitive impairment is also a recognized risk factor for increasing dementia. Seniors with the condition develop Alzheimer’s disease at much higher rates than those of the same age with sharper memories.

Earlier, the same group of researchers had found that after weight training, older women with mild cognitive impairment improved their associative memory, or the ability to recall things in context — a stranger’s name and how you were introduced, for instance.

Now the scientists wanted to look at more essential types of memory, and at endurance exercise as well. So they randomly assigned their volunteers to six months of supervised exercise. Some of the women lifted weights twice a week. Others briskly walked. And some, as a control measure, skipped endurance exercise and instead stretched and toned.

At the start and end of the six months, the women completed a battery of tests designed to study their verbal and spatial memory. Verbal memory is, among other things, your ability to remember words, and spatial memory is your remembrance of where things once were placed in space. Both deteriorate with age, a loss that’s exaggerated in people with mild cognitive impairment.

And in this study, after six months, the women in the toning group scored worse on the memory tests than they had at the start of the study. Their cognitive impairment had grown.

But the women who had exercised, either by walking or weight training, performed better on almost all of the cognitive tests after six months than they had before.

There were, however, differences.

While both exercise groups improved almost equally on tests of spatial memory, the women who had walked showed greater gains in verbal memory than the women who had lifted weights.

What these findings suggest, the authors conclude, is that endurance training and weight training may have different physiological effects within the brain and cause improvements in different types of memory.

That idea tallies nicely with the results of the other recent study of exercise and memory, in which lab rats either ran on wheels or, to the extent possible, lifted weights. Specifically, the researchers taped weights to the animals’ tails and had them repeatedly climb little ladders to simulate resistance training.

After six weeks, the animals in both exercise groups scored better on memory tests than they had before they trained. But it was what was going on in their bodies and brains that was revelatory. The scientists found that the runners’ brains showed increased levels of a protein known as BDNF, or brain-derived neurotrophic factor, which is known to support the health of existing neurons and coax the creation of new brain cells. The rat weight-trainers’ brains did not show increased levels of BDNF.

The tail trainers, however, did have significantly higher levels of another protein, insulinlike growth factor, in their brains and blood than the runners did. This substance, too, promotes cell division and growth and most likely helps fragile newborn neurons to survive.

What all of this new research suggests, says Teresa Liu-Ambrose, an associate professor in the Brain Research Center at the University of British Columbia who oversaw the experiments with older women, is that for the most robust brain health, it’s probably advisable to incorporate both aerobic and resistance training. It seems that each type of exercise “selectively targets different aspects of cognition,” she says, probably by sparking the release of different proteins in the body and brain.

But, she continues, no need to worry if you choose to concentrate solely on aerobic or resistance training, at least in terms of memory improvements. The differences in the effects of each type of exercise were subtle, she says, while the effects of exercise — any exercise — on overall cognitive function were profound.

“When we started these experiments,” she says, “most of us thought that, at best, we’d see less decline” in memory function among the volunteers who exercised, which still would have represented success. But beyond merely stemming people’s memory loss, she says, “we saw actual improvements,” an outcome that, if you’re waffling about exercising today, is worth remembering.