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There are lots of good reasons to exercise, like toning those biceps, the satisfaction of breaking a sweat, or just actually using that gym membership you got when you made that resolution. And exercising is good for your general health and wellness.

It can also make you happier. That's because working out doesn't just affect your body-fat percentage — it can also change the way you feel by boosting happy brain chemicals and buffering your response to stress. And the effects can be so dramatic that many psychologists think regular exercise can help treat disorders like anxiety and depression.

Lots of research studies over the past decades have drawn a clear link between exercise and positive feelings. And the mood-boosting effects of a single bout of exercise can stick around for up to 24 hours, according to some studies. Part of why you feel so good after exercise, counterintuitive as it might seem, is because exercise is stressful.

Technically speaking, exercise is a physical stress on the body, which means it activates the hypothalamic-pituitary-adrenal or HPA axis—the part of your nervous system that controls your body's stress response. One of the things it does is signal production of the stress hormone cortisol. Cortisol helps produce the physical changes you associate with stress or exercise, like elevated heart rate.

But it also contributes to a negative feedback loop that eventually shuts down the HPA axis. Levels of cortisol in your blood rise initially when you're stressed, but once they reach a certain level, they signal the HPA axis to relax. And it takes your body some time to reset everything before cortisol levels can rise again after that happens.

That means exercise can act as a buffer to other stresses that come shortly after, even if they're psychological rather than physical. For example, a 2015 study in the journal Psychoneuroendocrinology had 40 young men do what's called the Montreal. Imaging Stress Task.

Basically, you do math problems while a ticker shows your expected performance on a big screen, which is not exactly relaxing. The researchers found that when subjects ran on a treadmill for half an hour beforehand, they had lower cortisol levels during the test. But the happy feelings associated with exercise don't just come from handling other stresses better.

Working out increases your levels of endocannabinoids, the neurotransmitters linked to the so-called ‘runner's high.' They decrease anxiety by binding to cannabinoid receptors in the brain—yes, cannabinoid like cannabis, because they're same receptors the psychoactive compounds in marijuana interact with. Endocannabinoids also help rein in an overactive HPA axis, so that's another way exercise can make you more resilient to other types of stress. Working out also ups your levels of serotonin, a neurotransmitter involved in the regulation of mood and emotion.

The harder you work, the more serotonin you produce. That's especially interesting, because low serotonin is linked to disorders like depression and anxiety. In fact, many antidepressant medications work by directly or indirectly increasing levels of serotonin in your brain.

And another chemical, called brain-derived neurotrophic factor, or BDNF, also goes up during exercise. BDNF is like fertilizer for your brain. It helps neurons grow and form connections with other neurons, and generally improves brain health.

Researches haven't yet figured the exact link between BDNF and mood, but it might help by enhancing your neuroplasticity, the flexibility that allows your brain to reorganize when you learn or experience something. In depression, neuroplasticity is disrupted, which makes it difficult for the brain to compensate if important neural circuits become impaired. So elevating BDNF might help reverse or prevent that.

And, maybe unsurprisingly, antidepressants also tend to increase BDNF levels. All that said, the similarities between exercise and antidepressants don't mean they're the same. The studies that look at the effects of exercise on a molecular level are usually only measuring things in the short-term — like, right after you hop off the treadmill.

Which doesn't tell you much about how long the boost lasts. But the research is increasingly showing the long-term benefits of regular exercise, too. One study, published in 2017, examined the mental health and exercise habits of almost 34,000 Norwegians for more than a decade.

And the researchers found that people who didn't exercise had a 44% greater chance of developing depression compared to those who exercised 1-2 hours a week. Other research has found that — at least for mild to moderate depression — exercise can be just as beneficial as other treatment options. For example, a 2011 study in the journal Psychosomatic Medicine of over 200 adults diagnosed with depression found that exercise was just as effective as an antidepressant over a four month period.

Now, before you go out and swap your Paxil for Pilates, it's worth noting that there were some biases in this study. For one thing, the subjects were people who responded to an ad about research on treating depression with exercise, so a lot of them were very pro-exercise in the first place. The researchers also noticed that some people seemed anti-medication as a treatment.

All of which would have affected the results. But no matter how exercise compares to other treatment options, research has made it pretty clear that working out has all kinds of benefits for both your mind and body. So if you think you might be depressed, definitely see a doctor.

But if you're stressed about a project, or just feeling down in the dumps, getting a little bit of exercise might help. Thanks for watching this episode of SciShow Psych! If you want to learn more about that buzz you get from working out, you can learn more about that in our episode on why you get that runner's high. [♪ OUTRO ].