Environmental Health Australia: Is the gym IAQ affecting how hard you can train? Why fresh, filtered air matters

Gyms are one of the most challenging indoor environments to manage whenit comes to air quality. Unlike offices or homes, exercise changes how people breathe. During physical activity, breathing rates increase, and most air is inhaled through the mouth, bypassing natural nasal filtration. This allows pollutants and microorganisms to travel deeper into the lungs, increasing the risk of health impacts.

Research shows that many gyms have poorer indoor air quality (IAQ) than other public spaces. High occupancy, frequent cleaning, and limited ventilation are common issues. Pollutants of concern include carbon dioxide (CO2), particulate matter (PM), volatile organic compounds (VOCs), and occasionally formaldehyde and microorganisms. High CO2 levels indicate poor ventilation, leading to accumulation of exhaled air and increased infection risk. PM from dust resuspension during exercise and cleaning activities, penetrates deep into the lungs during heavy breathing. VOCs from cleaning agents, disinfectants, and personal products, irritate airways while high humidity and crowding favour fungal and bacterial growth.

Breathing risks

CO2 levels are a strong indicator of ventilation performance and IAQ. Ideally, they should stay below 800 ppm, as recommended by IAQ blueprint1. However, many gyms exceed this by a large margin. One Brazilian study reported CO2 concentrations over 5,500 ppm in a gym using split-system air-conditioning, which only recirculated air2. Similar findings have been reported in Europe and Asia, with Portuguese gyms recording over 1,250 ppm in 54% of cases3, and gyms in Taiwan peaking at 3,680 ppm during peak hours4.

Particulate matter is another concern. World Health Organization guidelines suggest PM10 should remain below 45 μg/m3 and PM2.5 below 15 μg/m3 (24-hour mean)(1, 5). Yet gyms often exceed these limits during classes. Some studies have recorded PM10 concentrations of 989 μg/m3 and PM2.5 peaks of 479 μg/m3 during high- intensity sessions(6). These spikes occur due to dust resuspension and the use of talcum powder.

VOCs are commonly linked to cleaning practices. During COVID-19 restrictions, aggressive disinfection routines caused VOC levels to exceed safe thresholds by up to eight timesthe recommended limit of 0.6 mg/m37,8. Materials used for flooring and decoration can also emit VOCs and formaldehyde, especially in humid environments.

Infection risks

High occupancy and close contact amplify exposure to infectious aerosols, particularly during peak times when ventilation is insufficient. Prolonged exposure also affects staff, while evidence suggests strenuous exercise may temporarily suppress immune function, further elevating vulnerability.These factors, combined with poorly ventilated spaces, make gyms critical environments for airborne infection transmission and associated health risks.

Why ventilation matters and how to improve it

Many gyms rely on split air-conditioning systems that only recirculate indoor air, which does little to control pollutant build-up. Central Heating, Ventilation and Air Conditioning (HVAC) systems perform better, but only if the system is mechanically bringing in fresh outdoor air and filters are effective. During COVID-19, disabling air-conditioning worsened comfort without significantly improving IAQ9.

The most effective solution is to provide fresh, filtered outdoor air continuously. Technologies such as Indirect Evaporative Cooling (IEC) systems offer a practical way forward. Unlike conventional systems, IEC units supply 100% fresh filtered outdoor air, cool it without adding moisture, and pass it through high-efficiency filters (such as MERV 13 or High-Efficiency Particulate Air (HEPA)). This allows gyms to maintain CO2 levels below 1,000 ppm and meet ASHRAE 241 standard of 40 L/s per person of equivalent clean airflow rate target, reducing energy use compared to traditional mechanical ventilation10.

Practical steps for gym operators

1. Monitor IAQ in real time, particularly CO2, as a ventilation and infection indicator.

2. Upgrade filtration in HVAC systems and consider portable HEPA units for high- density spaces.

3. Limit VOC sources by using low emission cleaning products and scheduling intensive cleaning outside peak times.

4. Control PM levels with HEPA-filtered vacuums and by avoiding talcum powder use.

5. Manage occupancy during peak periods to maintain air quality and comfort.

The bottom line

Gyms need stricter air quality measures than most indoor spaces because exercise amplifies exposure and infection risks. Fresh, filtered air – not recirculated air – is essential. Adopting systems like Indirect Evaporative Cooling, alongside real-time monitoring and better filtration, ensures gyms remain safe and healthy without compromising energy efficiency.

Sonali Deshmukh: Seeley International Pty Ltd., College of Science and Engineering, Flinders University. Emma Kuhn: College of Science and Engineering, Flinders University.

References

1. Morawska L, et al. (2024) DOI: 10.1126/science.adl0677

2. Andrade A, et al. (2018) DOI: https://doi.org/10.1007/ s11356-018-1822-8

3. Ramos CA, et al. (2014) DOI: https://doi.org/10.1016/j. buildenv.2014.08.026

4. Kuo P-Y, et.al. (2023), DOI: https://doi.org/10.3390/ engproc2023055056

5. WHO et.al. (2021), et.al DOI: https://iris.who.int/ handle/10665/345329.

6. Peixoto C, et.al (2023) DOI: https://doi.org/10.3389/ fpubh.2023.1310215

7. Climática PMdAedA, et.al. (2021) Retrieved

from: https://diariodarepublica.pt/dr/detalhe/ portaria/138-g-2021-166296490

8. Peixoto C, et.al. (2023) DOI: https://doi.org/10.3389/ fpubh.2023.1310215

9. Alonso A, et.al. (2021) DOI: https://doi.org/10.3390/ su13052699

10. Jones B, et.al. (2025) DOI: https://doi.org/10.1016/j. buildenv.2025.113318

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