Link between exercise intensity and risk of infection while training indoors

Until now, there has been no clarity on how exercise intensity affects the emission and concentration of aerosol particles in exhaled air. Using a new experimental setup, a research team from Munich has shown that aerosol emissions increase exponentially with intense physical exertion, so indoor sports activities result in an increased risk of infectious diseases such as COVID.

Before the study, it was known that the respiratory volume of untrained people increases from about 5 to 15 liters per minute at rest to more than 100 liters per minute during exercise. In fact, highly trained athletes reach levels of 200 l/min. It was also known that many people have been infected with the SARS-CoV-2 virus by exercising indoors.

However, it was not clear how exercise intensity was related to the concentration of aerosol particles in exhaled air and the actual number of aerosols exhaled by an individual per minute, and therefore on the potential risk of spreading infectious diseases such as SARS-CoV-2. However, this information is urgently needed, for example, to design mitigation measures for school gyms and other indoor sports facilities, fitness studios or nightclubs to prevent closures in case of serious infection waves.

New methodology offers individually measurable aerosol values

A team led by Henning Wackerhage, Professor of Exercise Biology at the Technical University of Munich (TUM), and Professor Christian J. Kähler, Director of the Institute for Fluid Mechanics and Aerodynamics at the Universität der Bundeswehr München, has developed a new research method to study these issues.

His experimental apparatus initially filtered out aerosols already present in ambient air. In the following ergometer stress test, the test subjects he inhaled the purified air through a special mask that covered his mouth and nose. 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 exhaled air could escape. The number of aerosol particles emitted per minute was then measured and directly linked to the current performance of healthy test subjects aged 18 to 40 years.

Moderate aerosol emissions at medium effort

In this way, the researchers were able to investigate for the first time how many aerosol particles an individual exhales per minute at various levels of exercise intensity. The result: aerosol emissions during exercise it initially increased only moderately to an average workload of about 2 watts per kilogram of body weight. Above that point, however, they increased exponentially. That means a person weighing 75 kilograms reaches that threshold with an ergometer reading of around 150 watts. This corresponds to a moderate effort for a casual athlete, perhaps comparable to the exercise intensity of a moderate jog.

Aerosol emissions from well-trained athletes were significantly higher than those from untrained test subjects at maximal effort due to their much higher minute ventilation. The researchers found no significant differences in particulate matter emissions between genders.

Protective measures are important for high intensity training

Although aerosol experiments only provide indirect insight into the amount of virus 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 overwhelm the immune system. medical care.

“Based on our results, we distinguish between moderate resistance training with an intensity of up to 2 watts per kilogram of body weight and high to maximum intensity training. Due to the strong increase in aerosol emissions at high-intensity workloads above that initial reference point, special protective measures are needed in case of a high risk of infections with serious consequences,” says study leader, Professor Wackerhage.

“Ideally, that kind of training would take place outdoors. If that’s not possible, tests should be done to ensure there are no infected people in the room. Participants should also maintain a proper distance and a system should be installed. high efficiency ventilation. to run. Also, the risks of infection are reduced by training at lower intensities and keeping sessions shorter. It could also be possible for young and fit athletes to wear masks while training.” With low workloads, such as easy to moderately intense resistance training, adds Professor Wackerhage, less protection is needed and the risk of infection can be controlled. through ventilation and distancing systems.

The study is published in Proceedings of the National Academy of Sciencesand the research team is conducting experiments to compare aerosol emissions in strength and endurance training and correlate them with the ages and physical characteristics of the test subjects.