You go to the gym to improve your health. The environment you are doing it in may be working against that in a way you have not considered.
Indoor environments consistently show higher microplastic concentrations than outdoor ones. Gyms, specifically, combine most of the factors that drive indoor microplastic accumulation: synthetic flooring, synthetic equipment surfaces, limited ventilation, and a room full of people wearing synthetic activewear that sheds continuously during high-movement activity. For regular gym-goers, the choice of non toxic gym clothes is one of the few variables directly within their control.
Why Indoor Microplastic Concentrations Are Higher Than Outdoors
Outdoor air is diluted by volume and dispersed by wind. Indoor air is not. Microplastic fibers shed from clothing, furniture, flooring, and equipment accumulate in enclosed spaces without the dispersal mechanisms that reduce outdoor concentrations. Research published in Environmental Science and Technology (Dris, R., et al., 2017) found that indoor airborne microplastic fiber concentrations were significantly higher than outdoor concentrations in paired samples, with synthetic textiles identified as the dominant source.
In a typical indoor environment, the primary contributors are furniture upholstery, carpeting, and clothing. In a gym, where dozens of people are in synthetic activewear performing high-intensity movement simultaneously, the clothing contribution is amplified by both the number of garments and the mechanical stress being applied to them.
What Happens When Synthetic Activewear Is Worn During Exercise
Synthetic workout clothes shed microplastic fibers during wear through mechanical friction between fabric and skin, between fabric layers, and against equipment surfaces. Napper and Thompson (2016), in Marine Pollution Bulletin, documented consistent microfiber release from synthetic fabrics under mechanical stress. The intensity of that stress during exercise, compared to casual wear, means the rate of shedding during a gym session is higher than during normal daily movement.
In an enclosed gym space, those shed fibers enter the air and stay there. Ventilation systems in most commercial gyms are not designed to capture particles at the size range of textile microfibers. The fibers settle on surfaces, are resuspended by movement and airflow, and are inhaled by everyone in the space, including people whose own clothing is not shedding significantly.
Inhalation Is the Primary Exposure Route in the Gym
During exercise, breathing rate and depth increase substantially. A person exercising at moderate to high intensity can inhale five to ten times more air per minute than at rest, meaning the volume of microplastic-containing air passing through the respiratory system during a gym session is significantly higher than during a sedentary hour in the same space.
Jenner et al. (2022), in Science of the Total Environment, detected microplastic fibers in human lung tissue from surgical patients, confirming that inhaled microplastic fibers reach and are retained in lung tissue. The gym combines elevated airborne microplastic concentrations with elevated inhalation rates, making it a higher-exposure environment than the same space would represent at rest.
The Floor and Equipment Dimension
Gym floors, particularly rubber and synthetic turf surfaces used in functional training areas, are themselves a source of microplastic particles. Rubber flooring made from recycled tires, widely used in weight rooms and CrossFit-style gyms, releases tire rubber particles and synthetic rubber microplastics through foot traffic and equipment use. Research published in Environment International (Panko, J., et al., 2013) documented rubber particle release from synthetic surfaces under abrasion.
During floor-based exercises, yoga, stretching, core work, the body is in direct contact with those surfaces. The combination of skin contact with synthetic flooring and ambient inhalation of airborne microfibers makes the gym a multi-pathway exposure environment.
The Variable You Actually Control
You cannot control the ventilation system at your gym. You cannot control what other people are wearing. You cannot control the flooring material. What you can control is what you are wearing, and for people who train regularly, that is a meaningful variable.
Each person wearing synthetic activewear contributes to the airborne microplastic concentration in the space. Choosing activewear made from cellulosic rather than synthetic polymer fibers reduces your personal contribution to that environment and eliminates the direct skin contact exposure that synthetic fabric creates during exercise. For a broader picture of how to reduce microplastic exposure across multiple daily sources, the steps compound meaningfully.
TENCEL Lyocell is a cellulosic fiber. It does not shed petroleum-derived plastic microfibers. Kaplan et al. (2014), in Fibers and Polymers, documented TENCEL's moisture management and thermal comfort performance in active wear settings, establishing that the functional case for non-synthetic activewear is not a compromise on performance. The Sempre Leggings are 92% TENCEL Lyocell and 8% spandex, with the spandex content stated because the full composition is the relevant information.
What This Means Practically
Going to the gym is still worth doing. The cardiovascular, metabolic, and mental health benefits of regular exercise are not in contest here. What the microplastics research adds is a reason to think carefully about what you wear while you are there, and to recognize that the gym environment itself is not neutral on this question. The research on how microplastics interact with hormones and the findings on microplastics and women's health extend this picture beyond the gym into systemic health effects worth understanding. For those considering the reproductive implications, the evidence on what microplastics mean for fertility covers the current state of that research.
The fiber in your leggings is not a passive choice. In a gym full of synthetic activewear, it is one of the few variables within your control.
Sources
Dris, R., et al. (2017). A first overview of textile fibers, including microplastics, in indoor and outdoor environments. Environmental Science and Technology.
Napper, I.E., and Thompson, R.C. (2016). Release of synthetic microplastic plastic fibres from domestic washing machines. Marine Pollution Bulletin, 112(1-2).
Jenner, L.C., et al. (2022). Detection of microplastics in human lung tissue using muFTIR spectroscopy. Science of the Total Environment, 831.
Panko, J., et al. (2013). Chronic toxicity of tire and road wear particles to water- and sediment-dwelling organisms. Ecotoxicology.
Kaplan, S., et al. (2014). Thermal comfort of lyocell and other fibers in active wear. Fibers and Polymers, 15(6).
