Think of the effects of running on the body and you undoubtedly consider obvious metrics of fitness: a slimmer waist and smaller hips, better muscle tone in the legs and butt, a stronger cardiorespiratory system, lower blood pressure. What may not occur to you is the interplay between running and that most vital of vital organs -- your brain. Make no mistake, however; running's effects of the central nervous system are numerous and pronounced.
If you've ever felt more mental clarity after being a regular runner for a while, the reason may be simple and anatomical: Aerobic exercise may literally cause your brain to grow. As reported in the Jan. 18, 2010 edition of the U.K. "Guardian," scientists at Cambridge University in England studied the effect of running on gray matter in mice and found that running caused a marked proliferation of neurons in a part of the brain called the dentate gyrus, which plays a major role in the formation of new memories. Mice given unfettered access to an exercise wheel scored far better on simple tests of memories than did non-exercising controls. So if you feel like your mind traps just a little more data than it did before you took up perambulating, you're probably not imagining it.
Even nonrunners have heard of "runner's high," in which distance runners achieve a state akin to a drug fugue. While running perhaps doesn't confer the same high as something illegal, the phenomenon is real and its neurochemical basis is well known. Until 2008, scientists had long suspected that running promotes the release of endorphins, the body's natural form of opioids, or morphine-like painkillers whose use is associated with a sense of extreme well-being. Then, researchers in Germany used neuroimaging to explicitly show that endorphins were released in greater amounts in response to a two-hour treadmill run. So there's a good reason a solid run can lift your spirits, and it's not merely psychological.
Serotonin is a neurotransmitter strongly associated with depression, with higher levels associated with a sense of well-being. In fact, an entire class of drugs, called selective serotonin reuptake inhibitors or SSRIs, is dedicated to combating depression. Various studies have shown that exercise increases levels of serotonin in various areas of the brain. In particular, exercise to the point of fatigue increases blood levels of tryptophan, the amino acid that is the immediate precursor to serotonin, and decreases blood levels of certain branched-chain amino acids, or BCAAs. Since BCAAs inhibit the entry of tryptophan into the brain, both of these effects are important, In any event, running may well exert a natural antidepressant effect through these mechanisms.
Dopamine is yet another neurotransmitter associated with mood -- in this case, not so much a sense of ordinary well-being as pleasure per se. It is also associated with movement, which is why dopamine deficiency in a critical part of the brain is the cause of Parkinson's disease, a disorder characterized by tremor and worse. Exercise has long been known to mitigate the symptoms of Parkinson's disease, and this observation has been supported by studies demonstrating the increased release of dopamine in response to exercise in rats. In addition, the increased sense of well-being associated with exercise may be mediated in part by dopamine.
- ScienceDaily.com: Runners' High Demonstrated: Brain Imaging Shows Release Of Endorphins In Brain
- Journal of Psychiatry & Neuroscience: How to Increase Serotonin in the Human Brain Without Drugs
- The Journal of Neuroscience: Effects of Treadmill Exercise on Dopaminergic Transmission in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Lesioned Mouse Model of Basal Ganglia Injury
Michael Crystal earned a Bachelor of Science in biology at Case Western Reserve University, where he was a varsity distance runner, and is a USA Track and Field-certified coach. Formerly the editor of his running club's newsletter, he has been published in "Trail Runner Magazine" and "Men's Health." He is pursuing a medical degree.