All forms of exercise have some health benefit. But if you’re interested in a healthier brain, a new study suggests, you should opt for a not-too-intense form of running.
Until quite recently, scientists thought that humans were born with a fixed number of brain cells. But new research has proven that hypothesis wrong. Some areas of the brain, such as the hippocampus, which is needed to store memories, continue to gain new neurons through adulthood.
More fascinating still is that studies in rodents have shown that running increases the rate of neurogenesis—creation of new neurons. Juha Ahtiainen, a physiologist at the University of Jyvaskyla in Finland, and his colleagues wanted to find out if other forms of exercise could do the same.
The researchers subjected two groups of lab rats—specifically bred to be either good or bad at aerobic exercises—to three sets of exercises, to mimic the human versions of endurance training, weight training, and high-intensity interval training (HIT) respectively. So some rats were given a running wheel, which they could use voluntarily. Some were made to climb walls with weights attached to them. Yet others—the HIT group—were put on a treadmill and forced to run at maximum capacity for three minutes, followed by two minutes rest, repeating the cycle for 15 minutes at a time. As a control, a fourth group of rats was left to lead sedentary lives.
After seven weeks of these exercise regimes, each rat’s brain was dissected and examined for production of new neurons in the hippocampus. Each form of exercise, as Ahtiainen and his colleagues report in the Journal of Physiology, had a different effect on the brains.
Those rats bred to be aerobic runners and left to run voluntarily formed the most new neurons. Those under the HIT regime formed some new neurons in the hippocampus, but much fewer than those running voluntarily. Finally, those that underwent weight-training had no more new neurons than those leading sedentary lives.
Although Ahtiainen doesn’t know the explanation for sure, he suspects that different kinds of exercise probably have different impacts on the levels of a protein, called brain-derived neurotrophic factor (BDNF), which triggers the production of new neurons. Previous studies have, for instance, shown that weight-training has no effect on BDNF levels in rat brains.
As for high-intensity interval training—increasingly popular with exercise enthusiasts—Ahtiainen thinks that it might just be a little too stressful. Stress is known to inhibit the production of new neurons.
Of course, the study only involved rats. But Ahtiainen told Quartz that these animal models have in the past provided a reliable indicator of what might happen in humans. The study also only looked at neurons in the hippocampus, so there is a chance that weight-training and HIT exercise might have beneficial effects elsewhere in the brain.
Still, whatever your favorite exercise, it’s clear there’s a good reason to include some running for your brain’s health. And, if you’re not much into exercise, you have now have one less excuse to not start.