Feeling mentally refreshed after a good bout of exercise might not just be a part of the post-workout euphoria; studies suggest certain types of exercises -- especially running -- can actually improve brain function by helping to create new brain cells.
It's not the first report to show exercise is good for the brain, but a study published in the Journal of Physiology in February suggests that running in particular could potentially help with neurogenesis, or the growth of new nerve cells.
Granted, the study was conducted on rats, not humans. However, researchers who led the study believe the findings might also apply to people.
The study looked at rats that were given different exercise regimes. One group did resistance training (by climbing a wall with weights attached to their tails); another did high-intensity interval training by sprinting on tiny treadmills; others ran on running wheels each day.
After seven weeks, researchers examined the rats' brain tissue to find that the group that ran at a moderate pace had shown "robust levels of neurogenesis" -- some even tripling the number of new neurons after exercise -- according to a New York Times story on the study.
"Their hippocampal tissue teemed with new neurons, far more than in the brains of the sedentary animals. The greater the distance that a runner had covered during the experiment, the more new cells its brain now contained," New York Times writer Gretchen Reynolds wrote in "Which Type of Exercise Is Best for the Brain?"
The study isn't aimed at knocking down certain types of exercises, such as high-intensity interval training or weight training, but rather, it suggests that moderate endurance workouts might be the best exercise for the growth of cells in the hippocampus, or the part of the brain that's key to controlling emotions, memories and the nervous system.
Amelia Dodd, a Murray State University exercise science department professor who holds a doctorate in physical therapy, said this isn't the only study on rats that has shown "sustained aerobic exercise increased neurogenesis compared to intense exercise, high intensity interval training and resistance training," she said.
Once upon a time, Dodd explained, it wasn't known that the brain and nervous system could adapt in ways that it's understood today. Rather, she said, people once believed that brain development stopped at a young age.
But today it's widely understood that the brain can adapt not only by creating new cells through neurogenesis, but its existing nerve cells can change the way they communicate, which is called neuroplasticity.
"In the past, it was believed that when nerve cells (neurons) die or were damaged, it was irreversible, especially in adults. It is now known that the brain has the ability to form new neural connections and reorganize throughout life if conditions are ideal and the brain is appropriately stimulated," Dodd said. "Studies are also now showing that in some regions of the brain, precursor cells remain and that with proper stimulation, these cells can grow, divide, differentiate and likely mature to form new neurons (neurogenesis). Stimulation of the brain can be applied through physical exercise or mental exercise."
The fact that exercise helps these processes isn't a new idea to Dodd, but she said there is more studying to be done to fully understand how physical exercise can stave off certain effects related to aging or other conditions, as well as encourage nerve cell growth.
Like using your brain to read or play a game of chess, Dodd noted that exercise can stimulate the brain, which in turn boosts its health.
"The brain is like a muscle. If you don't regularly engage in exercise (you lose muscle). The brain is kind of the same way: if you don't stimulate the brain, certain areas are going to be impacted or affected," Dodd said.
What the study on the rats indicates is that what Dodd called "sustained aerobics" can be particularly beneficial to the hippocampal part of the brain.
"To date, results utilizing human subjects have been mixed. Therefore, further studies to assess the effect of exercise on neurogenesis are needed," Dodd said. "It is known, however, that regular exercise has many positive effects on the brain that in turn improve attention, memory, mood, and cognition while also improving and/or maintaining brain tissue volume. Moderate intensity exercise appears to stimulate an increase in blood vessels in areas of the brain and decrease the inflammatory reactions while increasing or maintaining the volume of brain tissue."
While the study focused solely on distance running, with some of the rats putting in miles each day on a running wheel, Dodd pointed out that sort of sustained form of exercise could also carry over to a number of other aerobic activities, such as swimming or dancing. The key to the activity is to do it at a maintained pace over a period of time, unlike high-intensity interval training, which generally involves doing an intense exercise for a short period of time.
The weight training and more intense exercise may not have been found in this study to boost brain health in the hippocampal area, but those exercises could still help other parts of the brain.
And just because running might be good for the brain doesn't mean people should avoid resistance exercising or other forms of exercise, Dodd said, which she emphasized have their own positive effects on the body.
She cited the American College of Sports Medicine (ACSM) recommendations for getting in cardiorespiratory exercise (which helps both the heart and lungs). They include that healthy adults should:
n Try to get in at least 21/2 hours of moderate intensity aerobic activity five or more days of the week.
n Do resistance exercise that focuses on large muscle groups of the body for muscle fitness, flexibility training and neuromotor exercises. These exercises are recommended for two to three nonconsecutive days per week.
n Adults should perform flexibility exercise two or more days per week, Dodd said, which maintains or improves the motion of joints.
n Neuromotor exercise, or activities that focus on balance, agility, coordination and other motor skills, are recommended to be performed 20 to 30 minutes per day.
"The plethora of benefits of exercise emphasizes the critical need for individuals to develop lifestyle habits that incorporate the health-related components of fitness," Dodd said. "Even if unable to achieve the ACSM recommended levels of exercise, any activity is better than being inactive."
"I think it's all about being active, a variety of activities, just being well-rounded in terms of your engagement or exercise, so you can get all of the benefits," Dodd said.
She noted that running, despite its benefits, isn't for everybody. And even if the growth of new cells has yet to be solidified through further studies, there are plenty of other benefits of sustained exercise.
"Hopefully it promotes the growth of new cells, but even if it doesn't, (it improves) your mood, reduces stress, reduces diabetes and heart disease (risks) -- all of these things make it a critical thing to your life," she said. "(Choose) whatever mode that is going to challenge your heart and lungs to make some changes and improve your overall health."