Moving Outdoors Instead of Training Indoors: The Added Benefit of Green Exercise

Maybe you've been paying for months for a gym you hardly go to anymore. Maybe you feel guilty about it. And maybe you've already told yourself: I'm just too lazy.

May I offer you a different explanation? Maybe it's not you at all. Maybe it's the room.

Researchers have their own term for exercise in green spaces: green exercise. It means any physical activity in a natural setting, from a walk in the park to a mountain hike. For many years, researchers have been investigating whether this kind of movement can do more than the same movement indoors.

Exercise guidelines count minutes and intensity. That makes sense and is important. What an integrative view can add is a simple question: where do you move, and does it make a difference?

Same movement, different feeling: what the indoor vs. outdoor comparison shows

Do you know that moment after a walk in the woods? Your shoulders have dropped, your breathing is calmer, something in your head has sorted itself out. After an hour on the elliptical, you may feel good too. But different.

This is exactly the difference researchers have set their sights on. The idea is simple: people do the same exercise once indoors and once outdoors. Then researchers measure what differs.

Key point: The same exercise can feel considerably more pleasant outdoors. In a meta-analysis, the difference in enjoyment was large, with an effect size of 1.24 from ten comparisons involving 234 participants.

This apparently works on a small scale too. Focht at Ohio State University had 35 active young women walk for ten minutes at their own pace, once outdoors and once in the laboratory. Both walks lifted their mood. Outdoors, however, the women felt better, enjoyed the walk more and were more inclined to walk again.

From an effect size of 0.8 upward, experts usually speak of a large effect. A value of 1.24 is therefore remarkable for exercise research.

A 2019 review by Lahart and colleagues painted a similar picture. Single sessions in green surroundings could improve well-being and enjoyment, but not intensity or biological markers. After several weeks of training in green surroundings, perceived exertion in three studies was slightly lower than indoors. Overall, the authors rated the quality of the evidence as low.

Try it: take a session you would normally do indoors and move it outside for two weeks. Same duration, same pace. Just pay attention to how you feel during the session and afterwards.

And now you know why the same run can feel so different outdoors.

Stress hormones: what cortisol reveals about exercise in green spaces

Maybe you don't go running for your figure. Maybe you go to shake off the day: the pressure, the emails, the merry-go-round of thoughts. Then one question interests you most. Does exercise outdoors calm your stress system more than exercise indoors?

Cortisol is the best-known measure here. Imagine cortisol as the volume of your inner alarm system. In the morning it is high, so you can get going. Over the course of the day it drops, like the ebb after high tide. Under chronic stress, the dial often stays turned up too high.

Key point: Exercise itself can lower cortisol. Whether nature measurably adds something on top is an open question: in a randomized study with 42 adults, cortisol fell equally after mountain hiking and after the treadmill.

Does exercising outdoors lower cortisol more than exercising indoors?

This pattern comes up again and again. Peddie's meta-analysis found no clear differences in stress hormones between indoors and outdoors. Lahart, too, saw no consistent picture for biological markers.

Some studies nevertheless point to an additional effect. In a Norwegian pilot study, 14 employees exercised twice for 45 minutes each, either in green surroundings or indoors. In the nature group, the cortisol awakening response in the morning developed more favorably. For cortisol in the blood, by contrast, there was no difference.

In an Italian crossover study, 25 young men walked briskly for an hour each in green surroundings, in the city and indoors. In green surroundings, they felt more relaxed and perceived the effort as lower than indoors. Cortisol, heart rate and heart rate variability differed depending on the setting. However, the researchers found no difference in how these markers changed from before to after.

The picture becomes somewhat clearer when you look not at training, but at contact with nature in everyday life.

Large reviews point in a similar direction. In 2018, Twohig-Bennett and Jones at the University of East Anglia summarized a total of 143 studies. More green space in people's lives was associated with lower salivary cortisol, a lower heart rate and lower diastolic blood pressure. Many of these studies are observational, and a correlation is not yet a cause.

In Japan, a team led by Park measured physiological markers in a total of 280 young adults across 24 forests. Each participant walked for about a quarter of an hour and spent another quarter of an hour viewing the landscape, once in a forest and once in a city. In the forest, cortisol, heart rate and blood pressure were lower, and the calming branch of the nervous system was more active.

An Italian meta-analysis on forest bathing by Antonelli and colleagues also found lower cortisol in the forest groups. One detail is revealing: cortisol in those groups was already lower before the forest visit. The authors consider it possible that expectation and anticipation account for part of the effect. You can find more on this in my article Forest bathing: what happens in the body.

Adrenaline, the fast-acting stress hormone, might also respond. A Japanese team led by Li compared a three-day forest trip with a city trip in twelve healthy men, with the same amount of physical activity. Only after the forest trip did urinary adrenaline fall. With twelve participants, this is a hint, not a certainty.

If you want to reduce stress, what counts first is that you move at all. Then choose the place where it comes most easily to you. For many people, that's outdoors. You can find more on the interplay between exercise and an exhausted nervous system in my article Training despite burnout.

And now you know why the setting may matter less for cortisol than for mood.

Rumination, attention, a clear head: what might happen in the brain

You set off on your run, and in your head the midday meeting keeps going. Sentence by sentence. What you should have said. On the treadmill, facing a white wall, this merry-go-round often just keeps turning.

Experts call this circling rumination, or brooding in everyday language. It describes a thinking pattern that keeps circling around the same distressing thoughts. Rumination is considered a risk factor for depression.

Key point: Nature could turn down the volume on rumination. After 90 minutes of walking in green surroundings, rumination decreased. After 90 minutes of walking in the city, it did not.

Imagine this brain region as a meeting room where your worries hold their sessions. A forest path does not end the meeting. But it could turn the voices down.

Does it matter whether you're out in the city or in green surroundings? In a 2022 meta-analysis, Wicks and colleagues at the University of Essex compared exercise in natural and urban environments. Green settings showed large to moderate advantages for anxiety, fatigue, positive mood and vigor. For depressed mood, the advantage was small. Here, too, the risk of bias was high.

A common explanation goes like this: nature gently draws your attention without demanding it. Leaves in the wind, water, drifting clouds. Your concentration system gets a chance to recover while you move. This is plausible, but not conclusively proven.

Every now and then, leave your headphones at home when you train outdoors. Listen to the wind, the birds and your breath. Nature can only contribute something if it actually reaches you. If the interplay between exercise and mental health interests you, also read my article Exercise for depression and anxiety.

And now you know why thoughts sometimes come to you outdoors that had no room indoors.

Sticking with it: why the place could help shape your habit

January. Good resolutions, a new membership, new shoes. In February, you go twice a week. In March once, if things go well. And by April, only the monthly charge reminds you of your gym.

If you recognize yourself in this: you're in good company. And it's not a sign of weakness.

In my practice, I hear a version of this story again and again. People tell me that they forced themselves through gym sessions for a long time and find it easier to stick with it outdoors, whether walking, running or cycling. This is an observation from conversations, not a study. I cannot infer causality from it, because people who change the place often change other things too. But the observation fits with what researchers measure.

Key point: How exercise feels could help determine whether you stick with it. In a randomized study, exercise adherence was 97 percent outdoors and 91 percent indoors.

Rhodes and Kates at the University of Victoria reviewed 24 studies on exactly this question. Their finding: people who felt better during moderate exercise were more likely to be physically active later on. How they felt after training, by contrast, was hardly related to later behavior. So what apparently counts is how exercise feels while you're doing it.

Gym members themselves also provide clues. In Zurich, Hug and colleagues surveyed 319 members of fitness centers that offered both indoor and outdoor training. They experienced the outdoor locations as more restorative. And the more restorative they found a training location, the more often they had trained there in the previous 30 days.

In a review, Gladwell and colleagues at the University of Essex describe how the environment could motivate people to exercise and make it easier for them to get started. But they also name barriers that make access to the outdoors more difficult. And they describe how many people's connection to nature is changing.

Ask yourself honestly: where do you feel good while you're moving? Not afterwards, but during. This answer may be more valuable than any training plan. If you're going through menopause and want to build strength, you'll find more ideas in my article on strength training during menopause.

And now you know why sticking with it might be less a question of discipline than a question of place.

Light, air and green: three ingredients missing indoors

Think of a winter day at the office. You leave in the dark in the morning and come home in the dark in the evening. In between, artificial light, dry heated air, and then another hour at the gym under fluorescent tubes.

What you're missing is more than variety. Outdoors, three ingredients come into play that a room can hardly provide: daylight, fresh air and the green itself.

Key point: Outdoors is not automatically healthy. It depends on what kind of outdoors. On a busy London shopping street, the beneficial effects of a two-hour walk on the lungs and blood vessels were weakened. In the park, they were not.

Light: the timekeeper of your inner clock

Your body has an inner clock that resets itself to light every day. Daylight is the strongest signal for this. Even an overcast sky is usually brighter than a lit room.

Wright and colleagues at the University of Colorado investigated what happens when people go camping in summer and get only natural light. In everyday life with electric light, they got less sunlight during the day and more light in the evening, and their inner clock ran later. While camping, their inner clock aligned with the sun, and biological night began at sunset. The clocks of night owls shifted the most.

What this means for you: Exercising outdoors in the morning combines two things: training and a clear light signal for your inner clock. You can find more on this in my article on morning light and the inner clock.

And vitamin D? It's worth being honest here. In 1988, Webb, Kline and Holick exposed skin samples and a vitamin D precursor to sunlight, a laboratory experiment without living participants. In Edmonton, at about 52 degrees north latitude, no vitamin D was formed from October to March, even on cloudless days. Berlin lies at a similar latitude.

In winter, exercising outdoors is therefore no substitute for checking your vitamin D level. More on this in my article on vitamin D deficiency in winter.

Air: outdoors is not automatically green

In the forest, something else comes into play. In the forest air, the Japanese team led by Li found aromatic compounds from trees such as alpha-pinene and beta-pinene, which were barely present in city air. These so-called phytoncides are discussed as a possible building block of the forest effect. How much they matter in humans is an open question. You can find more on indoor and outdoor air in my article Fresh air and oxygen.

Green and water: what your eyes take in

In an analysis of ten British studies, which I'll go into in more detail in the next section, every green environment improved self-esteem and mood. Where water was involved, the effects were greater. A path along a river, a lake or a canal could therefore be a particularly good place for your round.

Plan your route deliberately: park instead of main road, riverside path instead of intersection, morning instead of darkness, if your everyday life allows it. In many cities, the nearest green space is closer than you think.

And now you know why light and air could be more than a backdrop.

How much nature does it take? The question of dose

Maybe you're thinking now: that's all well and good, but I live in the middle of the city. I don't have time for hours-long forest hikes.

The good news: the studies point to manageable amounts.

Key point: Even short sessions in green surroundings could bring the biggest jump. From about 120 minutes of nature per week, people in England more often reported good health.

How much nature per week makes sense?

In 2010, Barton and Pretty at the University of Essex analyzed ten British studies with 1,252 participants. Green exercise improved self-esteem with an effect size of 0.46 and mood with 0.54. The biggest jumps already appeared with short sessions. After that, the gain became smaller but remained positive. People with mental illness were among those with the greatest gains in self-esteem.

The last figure comes from Coventry and colleagues at the University of York. They analyzed 50 studies on nature-based activities, including 16 randomized studies. These covered gardening, green exercise and nature-assisted therapy. In the randomized studies, depressed mood and anxiety improved, and positive feelings increased. The most favorable duration was between 20 and 90 minutes. For physical health, the evidence was weaker.

When you have to train indoors

Sometimes there's no other way. Shift work, darkness, black ice, kids. Or you love your strength training on machines. That's perfectly fine. Exercise indoors remains valuable, as the comparisons with sitting already show.

In 2005, Pretty and colleagues had people run on a treadmill while images of landscapes and cities were projected onto the wall. Pleasant images, whether rural or urban, increased self-esteem more than training without images. Images of a spoiled landscape, by contrast, diminished the positive effect of training, including on mood.

Real green spaces seem to offer more, though. In Lahart's review, training in real green surroundings was more enjoyable than training with virtual nature. A spot with a view of greenery, walking to the gym instead of driving, stretching on the balcony: even small bridges to the outdoors could count.

And now you know why the big adventure matters less than a regular bit of green.

The four KPNI lenses on a run in the park

Imagine you're running through the park on a clear morning. What happens inside you, beyond heart rate and kilometers?

In clinical psychoneuroimmunology, KPNI for short, we look at how the nervous system, hormonal system, immune system and metabolism interact. A run in the park engages all four, and in a slightly different way than a run on the treadmill.

And now you know why the same round could engage quite different systems in you, depending on the place.

How solid the evidence is

Not everything in this article is equally well supported. So that you can put the statements into context, here is an overview of the levels. But first, three weaknesses that almost all studies share.

First: many studies look at only a single session or a few weeks. Second: participants are often young, healthy and few in number. Third: nature cannot be blinded. If you're running in the forest, you know it, and expectations could explain part of the effects.

When caution makes sense

Outdoors is not always cozy. Black ice in January, heat in July, pollen in April, darkness already in the afternoon.

These hurdles are not a reason to stay indoors. They are a reason to prepare well.

And now you know why good preparation doesn't make the outdoors smaller, but safer.

Three levers for your everyday life

Maybe you're wondering now: do I have to rebuild my whole training routine? No. Three directions are enough to start with.

And now you know why your next step might not lead to the gym, but out the front door.

Frequently asked questions about exercising in nature

More from the Natural Forces Guide

If exercise and health are on your mind