A major research topic during the ongoing coronavirus disease 2019 (COVID-19) pandemic has been the emission patterns of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 is mainly transmitted by aerosols produced during breathing, singing, shouting and other common activities.

Taken together, these factors play an important role in the transmission of SARS-CoV-2 indoors during group physical activities. A new PNAS study discusses the marked change in aerosol emissions over a range of physical exercises.

Study: Aerosol particle emission increases exponentially above moderate exercise intensity, resulting in overemission during maximal exercise. Image Credit: Kamil Macniak / Shutterstock.com

Introduction

COVID-19 is primarily an infectious viral respiratory disease; however, it can lead to multi-organ damage and death from acute respiratory distress syndrome (ARDS). As of May 26, 2022, over 6.3 million deaths have been reported worldwide as a result of COVID-19.

In an effort to reduce viral spread, non-pharmaceutical interventions (NPIs) like the use of masks for interactions with others, social distancing, restrictions on group activities including leisure and travel groups , as well as the closure of schools and businesses have been implemented. Additionally, many countries have declared a full lockdown for varying periods. However, this type of restriction also had counterproductive effects, such as a loss of physical fitness, emotional well-being, and overall resilience.

Group exercise indoors without very high ventilation promotes the spread of SARS-CoV-2 through the expulsion of respiratory droplets and aerosols. While droplets tend to fall to the ground within 1.5 meters of the source, aerosols can float in the air for much longer.

The concentration of aerosol particles in the exhaled air varies considerably from one individual to another. However, one in five people is considered a super-emitter because they exhale air containing more than 156 particles per liter of air. Talking, coughing, sneezing, singing and physical activity are all known to increase the number of aerosol particles emitted.

Airway dehydration also leads to increased aerosol emissions. This can happen during exercise or with high airflows.

High airflows are usually between 5 and 15 liters per minute at rest. Comparatively, during exercise, these airflows can increase between 100 and 200 liters per minute, depending on the level of training.

Previous research suggests that mild SARS-CoV-2 infection is associated with greater aerosol emission than its absence.

This suggests that people infected with SARS-CoV-2 who exercise will “breathe” more SARS-CoV-2 into a room, and uninfected people who exercise will inhale more SARS-CoV-2 particles. aerosol contaminated with CoV-2 compared to rest..”

In the present study, researchers are developing a method to assess aerosol concentration and emission in individuals from rest to maximal exercise.

Study results

The researchers found that the concentration of aerosol particles in both sexes increased tenfold, from 56 to 630 particles per liter at rest and at maximal exercise, respectively, using cycling ergometry. However, untrained individuals emitted significantly lower particle counts than those with endurance training, at 500 and 877 particles per liter during maximal exercise, respectively.

The highest concentration of aerosol particles was greater than 1000 particles per litre, which was observed in one male and two females. Particle size remained similar in females and males, as well as over the exercise range at less than 0.5 µm.

Airflow increased from nine liters per minute at rest to over 100 liters per minute at peak exercise in women. In men, the resting rate was 13, while the rate increased to 160 liters per minute at peak exercise. Ventilation was higher in males at peak rates. Training did not significantly affect peak ventilation.

Aerosol particle emission increased more than 130 times, with 580 particles per minute emitted at rest and 76,200 particles per minute emitted at peak exercise. The difference between trained and untrained people was about 85% and was in favor of trained people. The point at which aerosol particle emission exceeded 10,000 per minute was at an exercise intensity of 2 W/kg.

Additionally, the two individuals with the highest emission rates at rest also had higher emissions at peak exercise. It is important to note that no reliable pattern was observed in the relationship between these parameters.

Consequences

The striking increase in aerosol particle emissions with exercise, more than 100-fold with peak exercise, shows that peak physical performance is a primary contributing factor to aerosol overemission in people young and healthy of both sexes.

Aerosol particle emission is a function of exercise intensity; however, an exponential relationship is observed at and above an exercise intensity of approximately 2 W/kg. Notably, there was no observable relationship between aerosol particle emission at rest and during exercise.

The results of the study indicate the need for mitigation strategies to avoid transmission in indoor exercise groups. Additionally, the researchers also provide evidence supporting the value of this experimental method for measuring particle concentrations in a partial flow of exhaled air.

The researchers were also able to arrive at a more accurate estimate of the risk of viral spread from the emission of aerosol particles by individuals, particularly compared to those obtained using the more indirect method of concentration estimation. in exhaled or ambient air.

The extremely high increase in aerosol particle emission and exhaled air concentration during maximal exercise, together with the difference associated with endurance training, will need to be taken into account and will present a question for further studies. Some possible explanations for these observations include increased ventilation due to deeper breaths and exhalations, airway dehydration, changes in airflow velocity, and changes in fluids lining the lining of the airways. respiratory.

conclusion

Researchers in the current study recommend maintaining a distance of more than 1.5 meters between people during exercise, increasing room ventilation and keeping sessions between 45 and 90 minutes to limit exposure . During peak exercise, i.e. when overemission is likely, the room should be aired freely for 15 minutes between classes. It would also be beneficial if participants were tested for COVID-19 before each class.

Safety shields between individuals, masks, and movable air filters are other potential ways to reduce viral transmission in high-intensity exercise settings. However, the feasibility of these suggestions remains to be explored.

Aerosol particle emission increases moderately up to an exercise intensity of 2 W/kg and exponentially at higher exercise intensities. This information should be used to develop further data-based mitigation measures for indoor group exercises.”

Journal reference:

  • Mutsch, B., Heiber, M., Gratz, F., et al. (2022). Aerosol particle emission increases exponentially above moderate exercise intensity, resulting in overemission during maximal exercise. PNAS. doi:10.1073/pnas.2202521119.