When you're feeling stressed, going on a long run is perhaps one of the best things you can do to soothe frayed nerves. That much we know. Yet exactly how exercise helps moderate stress levels is less clear. Physical activity — whether you're shooting hoops or pumping iron — certainly gives your endorphins (those feel-good neurotransmitters swimming in your brain) a jolt. But that's just one part of the complicated stress-relief story.

A recent Venezuelan study published in the Journal of Neuroscience takes a look at why moving your legs (or any major muscle group, for that matter) helps curb all that icky anxiety that builds up from life's everyday irritations. In this case, researchers focused on a region of the brain called the ventral hippocampus, which "has been linked to anxiety regulation" but hasn't been explored in too much depth.

Big caveat: Scientists didn't examine the brains of runners. Or humans for that matter. Instead, they turned to the hippocampi of stressed-out lab mice. And since you can't saddle a four-legged rodent with a 30-year mortgage or rising tuition fees, researchers induced anxiety by dropping the little athletes into a bucket of cold water. (They're fine swimmers, it should be noted.)

Per Scicurious, "The authors wanted to examine how exactly exercise can protect the brain from anxiety-inducing (the sciencey word here is anxiogenic, impress your friends!) effects of stress." They examined the neural signals of mice that (1) were allowed to run in a wheel before taking the plunge, and (2) were sedentary before they were dropped in a bucket.

So what happened?

According to the paper's authors, gene markers associated with anxiousness increased noticeably in mice that didn't run, while mice that were forced to hit the exercise wheel beforehand failed to show a significant uptick of those same gene markers. The runner mice were also calmer and more collected than their non-athlete counterparts, especially after their unceremonious soak.

As for what's going on, researchers think the difference may be due to a neurotransmitter called GABA, which as Scicurious notes, is "often associated with inhibiting the activity of other neurons (many current anti-anxiety drugs on the market, for example, increase GABA signaling)."

Since runner mice expressed higher GABA levels than non-runners, researchers artificially suppressed the GABA receptors in their hippocampi. As was theorized, the runner mice with inhibited GABA levels were just as stressed as their sedentary pals after going for an unexpected swim.

Mind you, stress might isn't always a bad thing, especially when it comes to physical activity. A recent study from the University of Chicago found that elevated stress hormones can actually help give your athletic performance a tangible boost.

In any case, it's probably safe to add this study on anxiety regulation to the growing canon of evidence suggesting that exercise is an important ingredient for maintaining your mental health. So lace up your running shoes and hit the gym; unlike our four-legged pals, you probably have enough going on in your life that you don't even need to take a cold-water plunge.