By Michelle Voss
We all know that exercise is good for us. And this past holiday season, the market was awash with activity monitors like the FitBit and Nike Fuel Band to help you reach your fitness goals from the neck down. But what about from the neck up?
Although it may come as no surprise that exercise is good for your brain, we still do not have the metrics to guide optimal exercise for mental health. Today, the most common explanations for how exercise boosts mental health are that when we exercise we release endorphins that make us feel good and that exercise increases blood flow to our brains. Another explanation is that when we become more "physically fit," our brains become more fit. But the truth is that scientists still cannot fully explain the numerous mental health benefits of exercise. If we can't explain it, we don't know how to suggest the best types of exercise for your brain or how often you should do them, and we don't know how to biologically mimic exercise when it's not possible. The good news is that research from our team and others continues to make progress in understanding the connection between exercise and mental health.
Take, for example, the "super" protein BDNF (brain-derived neurotrophic factor). BDNF is thought of as a "super" protein because it seems to improve our brain's plasticity -- how it can change and adapt -- and the ability to repair itself following injuries. Researchers have found that muscle contractions that occur with exercise release antioxidants and other molecules into our blood circulation that interact with the brain and can potentially increase the presence of BDNF in the brain.
Although scientists have yet to fully map out how BDNF communicates between the body and the brain, numerous studies have documented that blocking BDNF signaling in the brain also blocks positive effects of exercise on learning and memory. From animal studies, we know these effects occur in a brain region called the hippocampus, which is a brain region that is critical for many types of learning and memory. However, we don't know if the same happens in humans. This will be important to find out: While on average the hippocampus starts to shrink at around age 60 and does so more dramatically for those who end up developing dementia in older age, it is possible the right dose of exercise-induced BDNF could help delay these age-related declines.
We also know through several studies that exercise results in almost immediate increases in BDNF expression in the brain, with researchers finding higher levels of BDNF in animals within the first hour of exercise and following just several days of running. These findings suggest the rise in BDNF likely plays a role in improved mental health, in addition to changes in physical fitness or blood flow in certain regions of the brain that likely require a more sustained exercise routine. Our team is working to connect how these quick exercise-related changes in BDNF in the periphery (e.g., muscle, blood) and in the brain relate to the long-term benefits of exercise on mental health.
If we can figure out the guiding principles of how exercise promotes improved brain health, and can translate them to humans, then we can optimize its benefit at the individual level and across the lifespan. Indeed, the power of exercise is that it naturally elicits a powerful regenerative response throughout many systems in the body that otherwise would suffer from the effects of aging or neurological disease. Anyone who has seen the ravages of dementia or brain injury knows that we must treat our brains with care; its degeneration or injury can change the very nature of who we are, and many times we would do anything to just be ourselves again.
As we continue to explore how best to delay or possibly prevent brain disease and injury, it's important to reflect on the many things we don't know. This includes understanding differences in how exercise affects the aging versus the developing brain, and differences between healthy adults and people fighting neurological disease. Knowing this information would be the first step in integrating brain health into accessible activity monitors.
And finally, we want to understand how long you can be inactive before the positive benefits of exercise start to diminish. For example, we know that you can lose much of your training gains on physical fitness with about two to three weeks of inactivity. Does the same timescale generalize to brain benefits?
So while we don't yet know exactly what guideline to suggest for exercising for brain health, we are getting closer. The federal government suggests 150 minutes a week of exercise that gets your heart rate up for improved overall health, and on average, studies support that this may improve brain and mental health too. But we still know very little about whether this is the optimal dose of exercise for brain health for different populations and exactly how the effects occur. Our research team and others will continue to work on these problems. In the meantime, we know that something is better than nothing. So, grab your favorite activity monitor and get moving: your brain will thank you.
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Michelle Voss, a cognitive neuroscientist, is an Assistant Professor in the Department of Psychology at the University of Iowa, where she is a member of the Aging Mind and Brain Initiative and directs the Health, Brain, & Cognition laboratory.
This post is part of a HuffPost Science series exploring the surge of new research on the human brain. Are you a neuroscientist with an insight to share? Tell us about it by emailing science@huffingtonpost.com.