By Markham Heid
May 07, 2014

Lace 'em up. Winter's over and some of the best running weather of the year has arrived. But depending on how much cardio (or couch surfing) you did during the colder months, your brain and body may react to that long run of yours in different ways. Here, what's going on during your extended bout of exercise.


Anticipating a challenge, your brain may have already signaled to your nervous system that it's time to start conserving resources, shows research from Harvard Medical School. As a result, your heart beats faster, and some of your blood is diverted from your stomach and digestive tract to your limbs, pumping your muscles full of the oxygen and nutrients they'll need to get the job done. (This is part of your system's fight-or-flight response, but more on that in a minute.) The diversion of blood away from your gut can cause a sensation of butterflies in your stomach or tingling in your arms or legs, the Harvard research suggests.


Your brain is receiving input from your body that it's getting a workout, which it interprets as a type of stress, shows research from Eduardo Portugal and colleagues at Brazil's Federal University of Rio de Janeiro. For out-of-shape runners, this stress can trigger a big release of the fight-or-flight hormone cortisol. On the other hand, trained athletes have a dampened cortisol response, at least in the early stages of a long run, Portugal explains.

Whether these stress reactions are mild or intense, your nervous system releases a protein called brain-derived neurotropic factor (BDNF), which stimulates regions of your brain related to learning, memory, and higher cognitive functions like decision making, shows a study from Texas tech University. This happens to help you better interpret the information you're receiving from your body (I'm working hard here!), and to make decisions about what to do next (Keep going? Stop?), the research indicates. Put simply, your brain recognizes that your body's under stress, so it takes steps to try to maintain normal conditions, Portugal explains. If you're out of shape, a heightened stress response will make it tough for you to push through the pain, his study suggests.


In response to continued physical exertion, your noodle experiences a flood of neurotransmitters whose type and amount depend on your level of training, research shows. If you're not used to running long distances, elevated levels of cortisol, as well as GABA (a hormone that blunts your brain's pleasure receptors) are in full control telling you to give it a rest, shows research from France. But if you're in shape, neurotransmitters related to your brain's reward centers (including endorphins) are blocking those GABA hormones, the same French research shows. This blockage allows the release of chemicals like dopamine, which give you a sense of pleasure and dull your sensitivity to pain, the study indicates. Your brain may also be enjoying an influx of the neurotransmitter norepinephrine, which increases alertness, Portugal says.

You may also be experiencing muscle cramping. Although a lot of runners believe this is caused by dehydration, it may be an issue of your brain directing secondary muscles to fire more forcefully, research suggests. As your primary running muscles weaken (and your form breaks down), your brain tells surrounding muscles to chip in. But those muscles aren't accustomed to working so hard, so they cramp, the research indicates.


Whatever kind of shape you're in, your elevated heart rate and blood pressure will continue to pump oxygen to your brain and body even after you've stopped running, which leaves you feeling sharp and energized, Portugal says. And unless you worked out to the point that all your feel-good brain chemicals are depleted, dopamine levels will remain elevated for a time, leaving you with a sense of pleasure, research shows.


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