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Reducing the risk of infectious diseases by doing vigorous exercise



The relationship between exercise intensity, emission, and concentration of aerosol particles (dust particles suspended in the air) in exhaled air is not well understood. Using a unique set of experiments, a research team in Munich has shown that greenhouse gas emissions increase exponentially with high levels of physical activity. These results suggest that indoor sports activities may increase the risk of infectious diseases, such as COVID-19.

Before this research, it was known that the respiratory volume of non-athletes during exercise is from 5 to 15 liters per minute and increases to more than 100 liters per minute at rest. In fact, well-trained athletes can reach 200 liters per minute. Also, it was shown that many people were infected with the SARS-CoV-2 virus (coronavirus 2 – acute respiratory syndrome) while working indoors.

However, it is unclear how exercise intensity is related to the number of airborne particles and the concentration of aerosol particles in exhaled air and thus the potential risk of transmission of infectious diseases such as SARS-CoV-2.

For example, school gymnasiums, gyms, and other indoor sports facilities are places where action should be taken to prevent a wave of infections. A team led by Henning Wackerhag, Professor of Sports Biology at the Technical University of Munich (TUM), and Professor Christian J. Kähler, director of the Institute of Fluid Mechanics and Aerodynamics at the Bundeswehr University of Munich, has found a new research method to investigate these questions.

Their experiment initially filtered the suspended particles in the ambient air. In the stress test, which was taken by an ergometer, the subjects inhaled purified air through a special mask that covers the mouth and nose. The intensity of the exercise gradually increased from rest to the point of physical exhaustion. The mask was connected to a two-way valve from which only exhaled air could escape.

Then, the number of aerosol particles emitted per minute was measured and directly related to the current performance of healthy people aged 18 to 40 years. Therefore, the researchers were able to investigate for the first time how many aerosol particles are exhaled per minute by a person at different levels of exercise intensity.

Result: Aerosol emissions during exercise initially increased only modestly and increased to an average workload of about 2 W/kg body weight. However, above that point, they increased exponentially. This means that a person who weighs 75 kg reaches that threshold with an ergometer with a workload of about 150 watts. This corresponds to an average effort for the average athlete, perhaps comparable to the intensity of an average run.

Aerosol emissions were significantly higher in well-trained athletes than in untrained athletes. The researchers found no significant difference in particle emissions between men and women.

Based on our results, we distinguished between moderate endurance training with an intensity of up to 2 watts per kilogram of body weight and high-intensity training up to the maximum. Professor Walkerhage, lead author of the study, says: “Because of the sharp increase in greenhouse gas emissions at workloads of higher intensity than the baseline, special protective measures are needed in case of high risk of infection with serious consequences, including being moved to the open air.”

If this is not possible, testing should be done to ensure that there are no infected individuals in that environment. Participants must also maintain proper distance and a high-efficiency ventilation system must be implemented. In addition, training with lower intensity and shorter sessions reduces the risk of infection. It may also be possible for fit young athletes to wear a mask during training.

At low workloads, such as light to moderately intense endurance exercise, less protection is needed and the risk of infection can be controlled through spacing and ventilation systems, adds Professor Walkerhage.


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