Why You Need to Exercise Outdoors: Part 1—The Problem With Pollution in Gyms

In this episode, learn the benefits of exercising outdoors, the problem with polluted gyms, and more. 

Ben Greenfield
5-minute read
Episode #239

Recently, I’ve been exercising outdoors far, far more than I usually do. As a matter of fact, these days I’m in the gym about an average of once every two weeks. This stands in pretty stark contrast to the years when I was a bodybuilder, spending 1.5-2 hours in the morning pumping iron at the health club, typically followed by another visit later in the afternoon or early evening.

Now, don’t get me wrong: if the only thing that keeps you physically active, exercising, and motivated to train or live healthy is a gym membership and a regular visit to your health club, then that’s far, far better than laying on the couch eating twinkies and watching Game of Thrones.gym

But at the same time, there are some big problems with gyms and some big benefits to being outdoors that you’re going to discover in this two-part episode. In this episode, you’re going to learn about the problem with gyms and tight indoor spaces where lots of people are exercising, and in the next episode, you’re going to learn about the potent fixes that nature can provide. You'll also get plenty of tips to exercise outdoors, no matter where you live.

The Problem With Gyms

Recent studies (a full list is provided at the end of this episode) have highlighted the fact that there are concerningly high levels of carcinogens in the air of the average fitness center, as well as significant amounts of harmful bacteria on the surfaces of fitness equipment such as treadmills and weight training machines.  

I’ve addressed the problem with air pollution in the episode Is Exercising in Pollution Bad For You?, and the takeaway message from that episode is that, compared to skipping exercise altogether, it’s still better to exercise even if you’re in a polluted area. But at the same time, the CDC, the EPA, and plenty of medical journals have found that exposure to air pollutants in urban areas is linked to higher rates of asthma and abnormal heart rhythms, and increases your risk of death from cardiovascular disease, respiratory diseases, and all causes. What this means is that if you actually do have the choice between, say, exercising in your backyard or a nearby park or forest versus exercising in the gym, you’d be far better off with the former.

And then there’s recent data showing that the indoor air quality in some fitness centers may be just as harmful to health as the air pollutants in urban areas. For example, one study last year in the journal Building and Environment found unacceptably high levels of carbon dioxide, formaldehyde and other volatile organic compounds (VOCs), and particle pollution in multiple indoor fitness centers.

Next, there’s carbon dioxide (CO2). Since expiration releases CO2, its levels significantly rise when there are lots of people huffing and puffing in a room, especially if that room is poorly ventilated. So, the more folks you cram into an indoor space running on treadmills, rowing, riding bikes, lifting weights, and jumping around, the worse the quality of air in that space. This is why I’m a bigger fan of home gyms than commercial gyms, and also a fan of getting in and out of a gym quickly by utilizing a strategy such as High Intensity Interval Training (HIIT). 

One study showed the highest levels of CO2 in an interior room used for indoor cycling spin classes. I’m not saying that these CO2 levels are toxic and going to kill you, but they’re not completely harmless either. This is all the more concerning when you consider the fact that most building owners (gyms often lease from building owners) save money by recycling used air instead of heating or cooling fresh air from outside.


All content here is for informational purposes only. This content does not replace the professional judgment of your own health provider. Please consult a licensed health professional for all individual questions and issues.

About the Author

Ben Greenfield

Ben Greenfield received bachelor’s and master’s degrees from University of Idaho in sports science and exercise physiology; personal training and strength and conditioning certifications from the National Strength and Conditioning Association (NSCA); a sports nutrition certification from the International Society of Sports Nutrition (ISSN), an advanced bicycle fitting certification from Serotta. He has over 11 years’ experience in coaching professional, collegiate, and recreational athletes from all sports, and as helped hundreds of clients achieve weight loss and fitness success.