You already know, if you work out regularly, that exercise helps you handle stress more effectively. You’re generally calmer and stay on an even keel when you work out consistently…and you feel more fidgety and anxious when you skip too many exercise sessions.

But there’s a puzzling paradox around the anxiety-reducing effects of exercise, and it has to do with what goes on in the brain. Basically, it’s this: Exercise is known to create an abundance of excitable neurons, especially in the hippocampus, a region of the brain involved in thinking and emotional responses. These kinds of neurons aid quick thinking and memory formation—but they also can fire at almost any provocation. If excitable neurons firing willy-nilly can induce anxiety, how does exercise reduce anxiety?


An intriguing new study offers some answers…and some inspiration.


The study included a series of experiments on adult mice. For six weeks, some mice were permitted to run on wheels to their hearts’ content…other mice had no access to running wheels.

Measuring anxiety: Previous research showed that, given the option, anxious mice tend to avoid open spaces. So to see whether the running mice were more or less anxious than the sedentary mice, mice from both groups were placed in a maze for five minutes. Some sections of the maze had high walls, creating a fairly enclosed environment…other sections were open. Sure enough, the running mice demonstrated less anxiety, spending about 50% more time in the open areas than the sedentary mice.

Counting neurons: Examining some of the mice’s brains, the researchers found that, compared with sedentary mice, the running mice had more new, excitable neurons in the dentate gyrus, an area of the hippocampus associated with anxiety regulation. These additional excitable neurons might seem to contradict the idea that exercise reduces anxiety—but hang on, because the researchers made another important discovery by purposely triggering stress…

Inducing stress: First, researchers locked the running wheels for one day to make sure that any changes in the mice’s brains would reflect their long-term running habit, not just the immediate effects of an exercise session. Next, some of the mice in each group were subjected to a stressful experience—swimming for five minutes in cold water (which mice do not enjoy). Brain examination then revealed that, compared with sedentary mice, the running mice had more of a kind of neuron called inhibitor neurons, which buffer the activity of the excitable neurons. In other words, these inhibitor neurons act like a security blanket, hushing and soothing the excitable neurons and fostering a sense of calm. The running mice also released more gamma-aminobutyric acid (GABA), a neurotransmitter that further tamps down the excitable neurons’ reaction and induces calmness.


These experiments help explain how exercise can, at the same time, create excitable neurons that promote quick thinking and memory and also prevent an overreaction to stress. Of course, the brains of mice and men (or women) are not the same—but they do share enough of the same properties to make this study a source of fascination (at least to the neuroscience enthusiasts amongst us).

Takeaway message: Okay, we all know that regular exercise is important for everyone. But are you the type of person who tends to feel anxious…or are you under a lot of stress? If so, whenever you’re tempted to blow off your workout, I urge you in particular to think about those little mice building their neurons and soothing away stress as they scampered merrily on their running wheels. Maybe the thought will inspire you to take a run, too.