Indoor exercise and poor indoor air, is it safe to work out?

Exercising indoors is not recommended with poor air quality. It increases your respiratory rate, inhaled volume, and the air penetrates deeper into the lungs. Because of this, exposure to harmful substances increases up to 7 times. To improve indoor air quality, increase ventilation, use an air purifier, and clean often.

Indoor air is often about 2 to 5 times more polluted than outdoor air, according to the US Environmental Protection Agency. Therefore, exercising indoors comes with a greater risk of inhaling air pollutants than outdoor exercise. So, let’s have a look at the risks of indoor exercise and what you can do to mitigate them.

I remember a story about outdoor air pollution during my air quality classes at the University. Two students from China told us that after a run through the streets of Beijing, their teeth had black stains. and after blowing their nose, the tissue colored black. Although Beijing is one of the most polluted cities in the world, this clearly shows that air pollution is something to be aware of when exercising.

For exercising indoors, outdoor air quality matters. Due to (natural) ventilation, the quality of the outdoor air affects indoor air quality. Therefore, is it a good idea to choose a time to exercise when outdoor air pollution is relatively low. This is mostly during the weekends when traffic is minimal. In general, it is best to exercise at 14:00 when air pollution is low due to low traffic. The overall cleanest air is found between 4:00 and 6:00, 12:00 and 16:00, and between 22:00 and 1:00.

The same is true for fitness centers with the addition that group sessions negatively affect indoor air quality.

Common indoor air problems at home

There are many compounds that reduce air quality and pose some kind of health risk. The health risk is dependent on the type of compound, the amount present in your indoor air, your exposure to them, and your overall wellbeing.

The most common air pollutants found indoors are:

  • fine dust particles
  • carbon monoxide (CO)
  • CO2 (carbon dioxide)
  • radon gas
  • volatile organic compounds (VOCs)
  • formaldehyde
  • mold

Unfortunately, most air pollutants are not noticeable since they are odorless and colorless. Therefore, it is wise to get to know how these compounds enter your air, what their potential health effects are, and most importantly, how to take preventive measures.

If you want to know everything about indoor air pollution, its adverse health effects, how to prevent it, and what you can do to clean your air, please read our article: The complete indoor air quality guide for your home.

Indoor exercise, opening a jar of pickles.
Afbeelding van Ryan McGuire via Pixabay

Common air pollutants in fitness centers

I found a study on indoor air quality in fitness centers, conducted in Lisbon, Portugal. Here, 11 fitness centers were tested on comfort parameters (temperature and humidity) and several air pollutants (fine dust, CO2, CO, VOC, and formaldehyde). (source)

This study found that especially CO2, VOCs and formaldehyde often exceeded the national limit values. These compounds were especially elevated during classes and cleaning sessions. Although the elevated levels during cleaning might sound surprising, cleaning agents often release hazardous gases when used.

So, it seems that if more people are together in a tight space, air pollution rises. This is obvious for CO2 as people breathe out CO2. Normally, CO2 is not that big of a concern as it is only harmful in very high concentrations. These are extremely rare. However, in small doses, it can contribute to a feeling of fatigue and loss of concentration. Something you would like to avoid when you are exercising.

Elevated levels of VOCs and formaldehyde are more concerning as they can cause irritation to eyes, nose and throat, and headaches. Formaldehyde is thought to contribute to an increased risk of cancer.

Increased risk during exercise

During exercise, people breathe more heavily. In this way, they inhale more often, they inhale a larger volume of air, and the air penetrates deeper into the lungs. In addition, people tend to breathe through their mouths more often during exercise.

Normally, you breathe about 15 times per minute. During exercise, this can increase to about 100 times per minute. In this way, the exposure to harmful airborne substances increases by up to 6 or 7 times.

On top of that, since you are breathing deeper, tiny airborne particles can penetrate deeper into the lungs. In this way, they come in contact with the more fragile parts of the lungs and can do more damage.

Young children are most at risk

Children are more susceptible to indoor air pollutants because they inhale more air and thus pollutants per kg of body weight than adults. Additionally, children’s airways are narrower than adults, so irritation and swelling of the airways can result in relatively greater airway blockage.

Do you need to start breathing in a different way because of poor air quality?

No, I do not think you need to breathe differently because of air pollution. However, breathing technique is an important factor for exercising in general. Although I am not a breathing or exercise expert, I do believe that it is normally recommended to breathe through the nose and out through the mouth. This is also the best way to make sure you naturally filter out large airborne particles with your nose.

Additionally, you might wonder if wearing a mouth mask helps against inhaling airborne compounds. Well, no, it does not. Mouth masks are designed to prevent the spread of moisture when you cough or sneeze. They cannot prevent airborne particles and gases from being inhaled.

How to improve indoor air quality for exercise

The first steps you can take to improve your indoor air quality are:

  • Increase ventilation. You should ventilate constantly and air the house regularly.
  • Make sure to clean often and thoroughly. Use natural cleaning agents to do so.

These two measures should greatly reduce indoor air pollution. However, if you are still uncertain about the quality of your air and want to take additional measures, there are several options:

When to exercise indoors

Levels of air pollution are not constant during the day and over the week. Therefore, the exact time you choose to do your exercise at home or at the gym can influence your exposure to air pollutants.

Since the outdoor air influences indoor air quality due to ventilation and airing, it is best to exercise when outdoor pollution levels are relatively low.

Normally, outdoor air quality is best during the early morning, in the middle of the day, and during the evening. This is because traffic is the largest source of air pollution, and has its peaks between 7:00 and 11:00 and between 17:00 and 21:00.

At what time is the air quality at its best?

The cleanest air is found at:

  • Between 4:00 and 6:00
  • Between 12:00 and 16:00
  • Between 22:00 and 1:00

The exact best time, when particulate matter pollution is the lowest, is around 14:00. (source)

In other words, just before the morning traffic starts, the air is relatively clean. In the middle of the day, traffic decreases and air pollution drops, before picking up again at 16:00. Also, late in the evening traffic has declined for several hours, and air pollution is again low.

At these times, air movement has had time to move air pollutants out of the city, or higher up into the air. Additionally, air pollutants may have settled, been taken up by water and plants, or have changed to other less harmful compounds.

On top of that, weekdays, because of low traffic, are the best days to exersice. If you cannot exersice during the weekend, or want to exercise more often, consider choosing a day close to the weekend. Normally, wednesday and thursday have the most polluted outdoor air and therefore reudce indoor air quality.

Air quality monitors help improve indoor air quality

To make sure you are always aware of the levels of CO2, VOCs, and other harmful substances in your house, an air quality monitor is an excellent tool. An air quality monitor can measure airborne chemicals, temperature, and humidity, depending on the device.

If you are interested in buying an air quality monitor, I would recommend choosing a model that measures a wide range of air pollutants. In this way, you never have to worry if you are missing just that one compound that is causing problems.

I found a Norwegian company called Airthings, that produces excellent air quality monitors. They are easy to operate (just wave your hand in front of the device) and send their data to an app on your phone.

Therefore, I recommend the Airthings Wave Plus. This air quality monitor not only measures humidity levels and VOCs but also CO2 levels, temperature, air pressure, and radon.

Discount on Airthings air quality monitor

By using this link to the Airthings Wave Plus air quality monitor you will get a discount of about 10%!

Which air purifier do I recommend?

There are many air purifiers available on the market. I looked at many different air purifiers and landed on the Coway Mighty. This is an affordable and quiet air purifier that lets you know when to replace its filters. On top of that, it has almost 4000 reviews on, of which 77% gave the maximum rating of 5 stars.

The Coway Mighty has four filters. A pre-filter to capture large particles, a deodorization filter, a HEPA filter, and a Vital Ion (ionizer).

The Coway Mighty, fit for rooms up to 361 square feet (33.5 square meter)

Is it better to go outdoors?

If its better to exercise outdoors or indoors highly depends on your specific situation. If you are living in a heavily polluted area, due to traffic or nearby industry, it is likely that your indoor air is less polluted than the outdoor air. However, if you can go out in nature, that is always the best option for air quality and overall wellbeing.

In addition, you do not have control over the quality of the outdoor air. Indoor air quality, however, can be controlled with an air purifier.