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After fracturing my humerus in an arm-wrestling match, something happened that I wasn’t prepared for. For the first time in my life, I lost the ability to exercise; the one thing that had always anchored my mental health. My mood began to unravel. The only solutions I knew were the ones I’d been taught in medical school: therapy or medication.

My experience isn’t unique; it reflects a much larger problem in how we currently treat depression. An estimated 1.17 billion people live with a mental disorder globally , and depression remains one of the most common. People with depression also face higher risks of other medical problems like obesity, diabetes, and heart disease. Yet our standard approach — medication, therapy, or both — leaves up to 30 to 50% of people without meaningful improvement and does little to address these physical comorbidities. This is why more holistic options, particularly exercise, deserve serious consideration.

What the evidence actually shows

Hundreds of clinical trials now show that exercise can significantly reduce symptoms of depression. For mild to moderate cases, its effects are generally comparable to medication or therapy. When exercise is combined with medications or therapy, the effects may even be additive . On a population level, even achieving just half the recommended amount of physical activity is linked to an 18% lower risk of developing depression .

Exercise treats depression through several mechanisms at once . It boosts brain neuroplasticity by raising brain-derived neurotrophic factor (BDNF) levels, which supports new neuron growth in the hippocampus, while also reducing chronic inflammation that can harm neurons. At the same time, it helps to regulate the body’s stress-response system and strengthen psychological resilience by boosting self-esteem, self-efficacy, and social connection. Together, these biological, mental, and social changes create a more resilient brain environment that makes depression less likely to take hold or persist.

However, we must be careful not to overstate the benefits. Headlines claiming that “exercise is 1.5 times more effective than medication or therapy” have spread widely, but they misrepresent the research . Those claims came from comparing effect sizes across studies of very different quality. When we look at higher-quality evidence and direct comparisons , exercise performs similarly to, but not dramatically better than, established treatments. Overhyping it risks damaging credibility in this important area of mental health.

Why exercise remains rarely used

If exercise is genuinely helpful, why isn’t it recommended more often? Exercise is already recommended as a first-line treatment for mild depression in major treatment guidelines . Yet a recent survey found that 92% of mental health professionals received no training in how to recommend exercise, and 41% said they never recommend it to patients.

There’s a clear disconnect between the evidence, the guidelines, and clinical practice. Imagine sitting across from your psychiatrist after being diagnosed with depression. If they simply said, “Just take this antidepressant,” you’d probably expect much more, such as the specific drug, the dose, how long to take it, and what side effects to watch for. Yet when it comes to exercise, vague advice like “just go work out” is still surprisingly common. Exercise deserves the same level of thought and structure we give to medication.

One practical way to do this is to use the FITT framework: Frequency, Intensity, Type, and Time. Instead of generic advice, a clinician might recommend something specific, such as: “Start with brisk walking three times a week for 20-30 minutes at an intensity where you can still talk.” This can then be adjusted as the person’s energy and fitness improve.

However, even with clear recommendations, depression itself can create major barriers. Fatigue and low motivation are among the most common, often making the idea of exercise feel impossible. These challenges are real but can be overcome by starting very small, building in social support or supervision, and combining exercise with other effective treatments.

What needs to change?

Real change requires more than simply acknowledging that exercise works. Clinicians need better training, starting in medical school and continuing through residency and beyond. They also need practical, up-to-date guidance on how to recommend exercise effectively.

That’s why I’m currently leading the development of new recommendations from the Canadian Network for Mood and Anxiety Treatments (CANMAT) and the International Society for Bipolar Disorders (ISBD) on the use of exercise in depression and bipolar disorder.

Training alone isn’t enough. We also need systems that make structured exercise programs practical, including direct referral pathways to qualified exercise professionals and insurance coverage, so that supervised programs or gym access can be integrated into care as easily as medication.

The evidence that exercise helps treat depression is strong. We don’t need more studies to prove it works. What we need now is to start treating it like the legitimate medical intervention that it is.

This article Exercise works for depression. So why isn’t it treated like real medicine? is featured on Big Think .

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A rocky planet orbiting in the habitable zone of a sun-like star may look like a perfect place for life to thrive — but not if it's too small to hold onto its atmosphere.

So, we may wonder: How much smaller Earth could be and still have its delightfully breathable atmosphere ? How small could an exoplanet be to sustain life as we know it?

With these questions in mind, University of California Riverside planetary scientist Michelle Hill and her colleagues recently simulated what happens to the atmospheres of different sizes of rocky worlds. The worlds tested were similar to Earth and orbited in the habitable zones around sun-like stars . It turns out for a world to maintain an atmosphere long enough for life to gain a foothold (a few billion years at minimum), it needs to be at least as big as Mars .

Narrowing down the search for life

The habitable zone — the area around a star where temperatures are right for liquid water to exist on a planet's surface — is prime real estate in the hunt for alien life. It's also a tough neighborhood for exoplanet atmospheres, because the closer a planet is to a star, the more ways in which radiation and stellar wind will try to strip away an atmosphere.

This is why Hill and her colleagues recently simulated how long it would take rocky, Earth-like planets of various sizes, in the habitable zone of a star like our sun, to lose their atmospheres. In other words, how much smaller could Earth, or a similar planet, be and still keep an atmosphere?

The answer turns out to be that an atmosphere-sustaining planet needs to be about 80% as wide as Earth, but could technically be as small as 60%. This offers astrobiologists a clue about which planets to focus on in the search for habitable worlds and signs of alien life.

"The plethora of exoplanets creates an interesting challenge in the search for potentially habitable planets," wrote Hill and her colleagues. "Of the many targets in the habitable zones of their star, which are the best candidates for follow-up observations with the aim of detecting biosignatures ?" In other words, astrobiologists now have almost too many planets to choose from and not enough telescope time to search them all. So, it's time to narrow the search.

One way to do that is to figure out which planets are most likely to be habitable — and for life as we know it, that habitability means having an atmosphere.

New exoplanets, like those orbiting TRAPPIST-1, are being discovered with staggering frequency. (Image credit: NASA's Goddard Space Flight Center) Modeling atmospheres — and volcanoes

Hill and her colleagues' "Smaller Than Earth Habitability Model" simulates the fate of atmospheres around digital versions of Earth. Some of the simulated worlds are exactly like ours but smaller, with the same chemical makeup and the same proportions of core, mantle and crust. Others have slightly different amounts of carbon, larger or smaller cores, or different starting temperatures. The model traces what happens to these worlds over a few billion years, based on two things: how quickly stellar wind and radiation strip away gas from the planet's atmosphere and how quickly volcanoes pump out gas (mostly carbon dioxide) to replace it.

The model is how the team realized a scaled-down version of Earth needs to be at least 80% as wide as true Earth (0.8 Earth radii) to maintain an atmosphere in the long run. Smaller planets tend to lose gas faster than volcanic eruptions can replace it.

That's because smaller planets have less gravity and weaker magnetic fields with which to hold onto their thin envelopes of gas. They also don't usually release enough gas from within to make up for the loss. Their mantles — the churning layer of magma beneath the crust — tend to release less volcanic gas over time, and their upper layers cool and harden much faster. The latter process cuts off volcanic eruptions much earlier in a planet's lifespan.

Smaller planets clinging onto atmospheres

By changing some of Earth's parameters, the team managed to get planets as small as 0.6 Earth radii to maintain a stable atmosphere. Carbon was the key: planets with more carbon in their mantles tend to release more carbon dioxide gas in eruptions, and that turns out to be the biggest factor (other than size) in whether a planet keeps its atmosphere.

"Carbon dioxide is a heavy molecule," Hill and her colleagues wrote, "which can make it a difficult molecule to lose. We focus on a pure carbon dioxide atmosphere as a best-case scenario for atmospheric retention." Of course, that's only a best-case scenario for some relatively simple forms of life, so your astrobiological mileage may vary.

It took tons more carbon than Earth contains to make a significant difference to the fate of a planet's atmosphere — but because it's theoretically possible for a planet to form with that much carbon in its makeup, that's useful knowledge. Planets with relatively smaller cores, and therefore relatively thicker mantles, also had better luck on the atmospheric retention front. Starting with a larger supply of radioactive elements, which decay and release heat into the surrounding rock, helped keep the mantle molten and the volcanic gases churning skyward.

Space volcanoes are widespread. For instance, Jupiter's moon Io has a pizza-like surface covered in volcanoes. (Image credit: NASA) Starting with a cooler mantle also helps — which sounds surprising. You'd think a hotter mantle would be more likely to spew volcanic gases into the atmosphere. Yet, a cooler mantle takes longer to start erupting in earnest, which means the planet gets to hold onto its reservoir of gases until its star is older and more settled.

Newborn stars are prone to violent bursts of radiation and plasma, which would sweep away the volcanic gas as fast as it erupted. With a cooler mantle and later eruptions, the planet gets to keep more of the erupted gas.

A second chance for airless worlds

There's still hope of life for smaller worlds.

Even planets that lose their initial atmospheres entirely — instead of gradually replacing them with things like carbon dioxide and methane — might have a second chance to build a new atmosphere.

Hill and her colleagues suggest that one way for a planet to regain its lost atmosphere could be comet and asteroid impacts, which might deliver volatile elements like hydrogen, oxygen and carbon. These elements can combine to form all sorts of atmospheric gases.

Such impacts could be especially helpful if they happen later in the star system's life, like after the star is past its youthful phase of intense flares.

"While smaller planets face greater challenges in retaining atmospheres, our model suggests that they can develop atmospheres under the right conditions," wrote Hill and her colleagues, so, "even those that initially lose their atmospheres should not be immediately discounted as potentially habitable worlds."

What's next?

Future simulations using the Smaller Than Earth Habitability Model could study worlds around smaller, cooler stars called red dwarfs — stars like TRAPPIST-1, which is home to at least seven rocky planets, with three of them in the habitable zone. These stars make up about 75% of the stars in our galaxy, and their relatively dim light makes it easier for telescopes like the James Webb Space Telescope (JWST) to capture images of starlight filtering through the atmospheres of planets that pass between Earth and their host stars.

Hill and her colleagues also hope to explore what happens to atmospheres around tidally-locked planets, or planets where tidal forces keep the interior hot and seismically active, similar to Jupiter's moon Io.

The researchers published their work in June in The Planetary Science Journal .

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If you own a mule and it happens to be named Cal, Gal, Hal, Pal, Val, or preferably Sal, grab your towrope and head over to Delphi, Indiana, to check out the Wabash and Erie Canal Park and Museum.

Opened in 2004, the museum features twelve interactive galleries tracing the history of the Wabash and Erie Canal from its inception and construction to its use and eventual closure. The park grounds have an extensive trail system and an 1850s pioneer village, where craftsmen ply their trades during canal season (mid-May through mid-September).

The Wabash and Erie Canal connected the eastern side of Indiana, near Fort Wayne, to the state's southwestern corner at Evansville on the Ohio River. Construction began near Fort Wayne in 1832, and when completed, the canal stretched 468 miles from Toledo, Ohio, to Evansville. Construction reached Delphi in 1840, and reports indicated that three mules pulled canal boats at speeds of 5 to 6 miles per hour. At the peak of construction in 1837, approximately 1,000 immigrants, primarily Irish, worked on the canal. Using only hand tools, they endured disease, snakes, and frequent accidents. Many were buried along the towpath they had helped create.

The canal had a tremendous impact on the growth of Indiana. When it began operating, the state's population was approximately 350,000. By 1840, it had grown to nearly 1 million. Ironically, canals are believed to have helped bring about their own demise by transporting the rails used to build the expanding railroad network across the United States. The last boat to travel the Delphi section of the canal was the Keystone State in 1874. The state then auctioned off the canal lands, and Indiana's canal era came to an end.