The link between exercise intensity and infection risk

Summary: The researchers identify the level of exertion at which the emission of aerosol particles increases dramatically, and provide an explanation for why exercise intensity is associated with transmission.

source: Tom

Prior to the study, the respiratory volume of untrained subjects was known to rise from about 5-15 liters per minute at rest to more than 100 liters/min when exercising. Highly trained athletes reach levels of 200 l/min.

It has also been known that many people have contracted SARS-CoV-2 when exercising indoors.

However, it was not clear how exercise intensity was linked to the concentration of aerosol particles in exhaled air and the actual amount of aerosol exhaled per minute, and thus to the potential risk of spreading infectious diseases such as SARS-CoV-2.

This information is urgently needed, for example to design mitigation measures for school gyms and other indoor sports facilities, fitness studios or discos to avoid closures in the event of dangerous waves of infection.

New methodology provides individually quantifiable aerosol values

A team led by Henning Wackerhage, Professor of Exercise Biology at the Technical University of Munich (TUM), and Professor Christian J. Kahler, Director of the Institute for Fluid Mechanics and Aerodynamics at the University of Bundeswehr in Munich, has developed a new investigative method to study these questions.

Their experimental device initially filtered the aerosols already present in the surrounding air. In the post-potentiometer test, test subjects inhaled fresh air through a special mask covering the mouth and nose.

The intensity of the exercise was gradually increased from rest to the point of physical exhaustion. The mask is connected to a two-way valve through which only exhaled air escapes. The amount of aerosol particles emitted per minute was then measured and directly related to the current performance of healthy 18-40-year-olds.

Moderate aerosol emissions at medium effort

Thus the researchers were able for the first time to investigate how many aerosol particles an individual exhaled per minute at different levels of exercise intensity.

The result: aerosol emissions during exercise initially increased only moderately until the average workload was approximately 2 watts per kilogram of body weight. Above that point, it rose exponentially.

This means that an individual weighing 75 kilograms reaches this limit at an accelerometer reading of about 150 watts. This corresponds to the moderate effort of the average athlete, and is perhaps comparable to the exercise intensity of moderate jogging.

Aerosol emissions of well-trained athletes were significantly higher than those of non-maximally trained subjects due to micro-ventilation. The researchers found no significant differences in particulate emissions between the sexes.

Protective measures are important for high-intensity training

Although aerosol experiments provide only indirect knowledge of the amount of viruses in exhaled air, the study suggests useful starting points for managing indoor activities when a wave of infection combined with a poorly immunized population threatens to flood the health care system.

“Based on our findings, we distinguish between moderate endurance training at an intensity of up to 2 watts per kilogram of body weight and training at maximally high intensity. Because of the sharp rise in aerosol emissions at high intensity workloads,” says study leader Professor Wackerhage. Above this initial criterion, special preventive measures are needed in the event that there is a high risk of infection with severe consequences.”

This shows a man and a woman doing sports
The intensity of the exercise was gradually increased from rest to the point of physical exhaustion. The image is in the public domain

“Ideally, this type of training would be taken outside. If this is not possible, testing should be done to ensure that there are no infected personnel in the room. Participants should also maintain an appropriate distance and operate a highly efficient ventilation system.

In addition, the risk of infection is reduced by training at a lower intensity and by keeping sessions shorter. It may also be possible for young athletes who are in good shape to wear masks during training.”

Professor Wackerhage adds that in low workloads such as easy to medium-intensive endurance training, less protection is needed and infection risks can be controlled with spacing and ventilation systems.

The research team is currently conducting experiments to compare aerosol emissions in strength and endurance training and correlate them with test subjects’ ages and physical characteristics.

see also

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About this exercise and infection research news

author: Henrik Boden
source: Tom
Contact: Henrike Boden – TUM
picture: The image is in the public domain

original search: open access.
Aerosol particle emission increases significantly above moderate exercise intensity resulting in superior emission during maximum exerciseWritten by Henning Wackerhage et al. PNAS


Aerosol particle emission increases significantly above moderate exercise intensity resulting in superior emission during maximum exercise

Many airborne pathogens such as SARS-CoV-2 are transmitted indoors via aerosol particles.

During exercise, pulmonary ventilation can increase more than 10-fold, and therefore, exercisers excrete more air containing aerosols. However, we do not currently know how exercise affects the concentration of aerosol particles in exhaled air and the overall emissions of aerosol particles.

Accordingly, we developed a method to measure in parallel the aerosol particle concentration in expired air, pulmonary ventilation, and aerosol particle emission at rest and during a graded exercise test to exhaustion. We used this method to test eight women and eight men in an observational study.

We found that the concentration of aerosol particles in the terminated air was significantly increased from 56 ± 53 particles/l at rest state to 633 ± 422 particles/l at maximum density. Aerosol particle emission per subject significantly increased by a factor of 132 from 580 ± 489 particles/min at rest to a superior emission of 76,200 ± 48000 particles/min during maximal exercise.

There were no gender differences in the emission of aerosol particles, but the endurance-trained subjects emitted significantly more aerosol particles during maximal exercise compared to the untrained subjects. In general, the aerosol particle emission increased moderately up to exercise intensity ∼2 W/kg and then exponentially thereafter.

Together, these data may partly explain superspreader events especially during high-intensity group exercise indoors and suggest that robust infection prevention measures are needed especially during exercise at an intensity exceeding 2 W/kg.

Investigations into influencing factors such as airway and whole-body hydration status during exercise are needed to generate aerosol particles.