Overview: Researchers identify the level of exercise at which aerosol particle emissions increase exponentially, providing an explanation as to why exercise intensity may be linked to infection transmission.
Before the study, tidal volume for untrained people was known to increase from about 5-15 liters per minute at rest to over 100 liters/min during exercise. Highly skilled athletes even reach a level of 200 l/min.
It was also known that many people were infected with the SARS-CoV-2 virus while exercising indoors.
However, it was unclear how exercise intensity was linked to the concentration of aerosol particles in the exhaled air and the actual amount of aerosols a person exhaled per minute and thus to the potential risk of spreading infectious diseases such as SARS-CoV-2.
However, this information is desperately needed, for example to design mitigating measures for school gyms and other indoor sports facilities, fitness studios or discos to prevent shutdowns in the event of serious waves of infection.
New methodology yields individually measurable aerosol values
A team led by Henning Wackerhage, professor of exercise biology at the Technical University of Munich (TUM), and Prof. Christian J. Kähler, director of the Institute of Fluid Mechanics and Aerodynamics at the Universität der Bundeswehr Munich, has a new research method to answer these questions. to study.
Their experimental device initially filtered the aerosols already present in the ambient air. In the subsequent ergometer stress test, the subjects inhaled the purified air through a special mouth and nose mask.
Exercise intensity was gradually increased from rest to the point of physical exhaustion. The mask was connected to a two-way valve through which only the exhaled air can escape. Subsequently, the amount of aerosol particles emitted per minute was measured and directly linked to the current performance of the healthy, 18-40-year-old subjects.
Moderate Aerosol Emissions at Moderate Exercise
This enabled the researchers to study for the first time how many aerosol particles are exhaled per minute by a person at different levels of exercise intensity.
The result: The emission of aerosols during exercise increased only moderately to an average load of about 2 watts per kilogram of body weight. Above that point, however, they rose exponentially.
That means that a person weighing 75 kilograms reaches that threshold at an ergometer reading of about 150 watts. This equates to moderate exercise for a casual athlete, perhaps comparable to the exercise intensity of moderate jogging.
The aerosol emissions of well-trained athletes were significantly higher than those of untrained subjects at maximal exercise due to their much higher minute ventilation. The researchers found no significant differences in particulate emissions between sexes.
Protective measures are important during intensive training
While the aerosol experiments provide only indirect knowledge about the amount of viruses in exhaled air, the study suggests useful principles for managing indoor activities when a wave of infection combined with a poorly immunized population threatens to overwhelm the health care system.
“On the basis of our results, we distinguish between moderate endurance training with an intensity of up to 2 watts per kilogram of body weight and training of high to maximum intensity. Due to the sharp increase in aerosol emissions at high workloads above that initial benchmark, special protective measures are needed at a high risk of infections with serious consequences,” said study leader Prof. Dr. Wackerhage.
“Ideally, that kind of training would be moved outside. If that is not possible, tests should be performed to ensure that there are no infected individuals in the room. The participants must also keep sufficient distance and a high-efficiency ventilation system must be running.
“In addition, infection risks are reduced by training at lower intensities and by keeping sessions shorter. It may also be possible for fit, young athletes to wear masks during training.”
At a low load, such as light to moderately intensive endurance training, adds Prof. Wackerhage, less protection is needed and the risk of infection can be controlled by distance and ventilation systems.
The research team is currently conducting experiments to compare and correlate aerosol emissions from strength and endurance training with age and physical characteristics of subjects.
About this exercise and news about infection research
Author: Henrike Boden
Contact: Henrike Boden – TUM
Image: The image is in the public domain
Original research: Open access.
“Aerosol particle emission increases exponentially above moderate exercise intensity, resulting in superemission during maximal exercise” by Henning Wackerhage et al. PNAS
Aerosol particle emission increases exponentially above moderate exercise intensity, resulting in superemission during maximum exercise
Many airborne pathogens, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are transmitted indoors via aerosol particles.
During exercise, lung ventilation can increase by a factor of 10, and therefore athletes will exhale a larger volume of aerosol-containing air. At the moment, however, we do not know how exercise affects the concentration of aerosol particles in the exhaled air and the total emission of aerosol particles.
Therefore, we developed a method to parallel measure the concentration of aerosol particles in exhaled air, lung ventilation and aerosol particle emission at rest and during a graduated exercise test until exhaustion. We used this method to test eight women and eight men in a descriptive study.
We found that the concentration of aerosol particles in exhaled air increased significantly from 56 ± 53 particles/liter at rest to 633 ± 422 particles/liter at maximum intensity. The emission of aerosol particles per subject increased significantly by a factor of 132 from 580 ± 489 particles/min at rest to a superemission of 76,200 ± 48,000 particles/min during maximum exercise.
There were no sex differences in the emission of aerosol particles, but subjects who did endurance training emitted significantly more aerosol particles during maximal exercise than untrained subjects. In general, aerosol particle emissions increased moderately up to exercise intensity ∼ 2 W/kg and exponentially thereafter.
Together, these data may partially explain superspreader events, especially during high-intensity indoor group training, and suggest that strong infection prevention measures are needed, especially during exercise at an intensity greater than ∼2 W/kg.
Research into influencing factors such as respiratory and whole-body hydration status during exercise on aerosol particle generation is needed.