Safely Sweating as Gyms Reopen

Photo: Personal Archive, Used with Permission

By Janet von Konsky Miller, MPH


Today marks the 1-year anniversary of the Santa Clara County Shelter in Place (SIP) order. For 365 days we have been social distancing. We have become used to days filled with Zoom meetings and screen time. With all this added screen time, finding creative ways to remain physically active has become more important than ever.

I recently heard the term “exercise snacks”1 to describe short physical activity breaks during the day. To accommodate increased computer time, I often take my “exercise snacks” outdoors with short neighborhood walks or garden puttering. For some, remote work means less time spent commuting in traffic. Substituting this commute time with physical activity is another way to keep the body moving. Standing desks and walking meetings are among other ideas for detaching from that chair.

But what about working up a sweat?

With gym doors closing to help mitigate SARS-CoV-2 transmission, the economy has experienced sky rocketing home gym equipment sales, new virtual gym technologies, and rising online streaming and fitness app options.2 Despite this, many have found it difficult to stay active. One multinational study of 1047 adults found that time spent in sedentary activity increased 28% and frequency of physical activity decreased 24% during shelter in place orders.3

While the fitness and wellness industry quickly pivots to provide pandemic exercise options through technology, embracing new technologies is nothing new to the fitness and wellness industry. Jack LaLanne used the blossoming television era in the 1950s to advocate for fitness and lead exercises over the TV screen.4 In the late 1960s, Kenneth Cooper introduced the term “aerobics”5 and Jackie Sorensen and Judi Sheppard Missett set exercise routines to music introducing aerobic dance and Jazzercise, respectively.6,7 This paved the way for home VHS workouts in the 1980s with fitness celebrities like Jane Fonda, Richard Simmons, and many others. As the popularity of step aerobics exploded and spinning dawned on the scene in the 1990s, DVD technology soon replaced VHS tapes.8 Today, DVD and VHS have been filed away in the history books as streaming and fitness apps take to the mainstage.  The music that group exercise instructors used over time also adapted to new technologies beginning with vinyl and progressing to cassette tapes followed by CDs. Now, exercise class music is downloaded and accessed through the instructor’s electronic devices. Wearable heart rate tracking technologies introduced in the 1970s have developed and become more sophisticated over time to motivate, monitor, and track the exerciser’s progress. While not an exhaustive list, this illustrates some ways the fitness and wellness industry has been influenced by technology.

While the pandemic has nurtured the industry trends of online apps and virtual training, what is in store for the industry as we look toward a post-pandemic future? As we reach the 1-year social distancing anniversary, Santa Clara County has re-opened gyms at a 10% capacity and will increase this to 25% capacity when the county moves from red into an orange level tier status.9 Some gyms have the space available for additional outside exercise. The California Department of Public Health suggests personal training and group exercise modifications to ensure social distancing is maintained.10

The question remains: How safe is it to go back to the gym? 

In February of 2020, 27 exercise instructors employed at 12 gyms attended a 4-hour workshop in South Korea. Of the 27 instructors, 30% were positive for SARS-CoV-2 despite a lack of symptoms. Through contract tracing, 112 COVID-19 cases were connected to these instructors, over half of which were from exercise class participation and the rest due to transmissions to family and coworkers. Note that this report indicates that transmission occurred prior to initiating pandemic restrictions.11

In June of 2020, an instructor taught a group cycling class at a gym in Hawaii. No one, including the instructor, wore masks. The instructor was symptom free at the time of class, but began experiencing symptoms within hours after class. All 10 class participants were diagnosed with COVID-19 the following week. Six of these participants had taken a class with the same instructor along with 4 others on the previous day, but the 4 others remained free of COVID-19. Another instructor who contracted COVID-19 from the first instructor trained 5 personal training clients and 9 group exercise clients over the 2 days before symptoms began, transmitting the virus to 10 of these clients. No masks were worn in any of these contacts.12

A Chicago gym offered 8 high intensity group exercise classes over a 1-week period at a reduced (25%) capacity during August of 2020. Face masks were required to enter the gym but not during classes. During this period, a COVID-19 outbreak occurred. Out of 91 people exposed, 81 were interviewed. Of those interviewed, 55 had contracted COVID-19. It is discouraging to learn that 4 of every 10 of these individuals attended an exercise class the day symptoms began or thereafter, with 3 who attended class with a positive COVID-19 diagnosis.13

While these cluster cases are alarming, it is important to look at what we know about SARS-CoV-2 transmission.

As one breathes, respiratory droplets are dispersed into the air. If these droplets are large enough, they fall quickly to the ground. Therefore, larger droplets infected with SARS-CoV-2 will be capable of transmission to another if the other is close enough to contact the droplet before it falls.14,15 A droplet that has fallen to the ground can reenter the air if the space is disturbed.16 An exercise class, therefore, may be capable of sending these fallen particles aloft, keeping them in the air.15 Larger droplets may evaporate into smaller droplets and the smaller the droplet, the longer it lingers in the air. The longer it lingers in the air, the greater the chance for contact by a new host.14,15

The amount of viral contact, or load, is also a consideration with SARS-CoV-2 transmission. A sneeze can project 10,000 droplets into the surrounding environment, far more than a cough at up to 1000 droplets. While talking is far less yet at 50 droplets, it has the potential to produce cumulatively more because it is more continuous than a cough or sneeze. No numbers exist specific to droplets in exercise exhalation, and it is suggested that numbers will likely vary between individuals. Virus infected respiratory particles exhaled by individuals can build up in indoor environments.15

If amount and size of droplets projected into the environment influences transmission, then inadequate facility ventilation becomes an important transmission mitigation factor.14  The number of people in the room, the amount and velocity of the fresh air contributed to the room, the amount of extracted air that is recirculated, the air cleaning and filtering technique, and the placement of the vents may all impact the particle concentrations in a room.14,17 In addition to closing group classes or limiting class size, the CDC recommends that exercise facilities maximize fresh air availability and filtration as well as maintain a 40-60% humidity level during the pandemic.18 The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) clarify that ventilation systems management cannot eradicate risk of viral transmission but instead reduce risk as a part of risk management.They recommend not only maximizing fresh air when weather permits, but also a continuous air filtration with a MERV-13 filter system.19 (MERV ratings designate filtration efficacy based on size of particles. The higher the number the smaller the particulate filtered, but using a rating higher than the system can handle reduces effectiveness of the system.)20 Portable air cleaners are suggested by the ASHRAE as a supplemental system option.19 UV germicidal radiation may not be an option for cleaning air as exposure is harmful to humans.21 In addition, the CDC recommends against floor fans that direct air flow onto members.18 Comparatively, Blocken and colleagues (2020) report recommendations established in the Netherlands with ventilation flow at 70% greater in Dutch fitness facilities compared to other stores and offices. Dutch building guidelines suggest ventilation systems replace the air in a gym 6 times per hour and in aerobics rooms 8 times per hour. In cycling classes, they suggest air is replaced 10 times per hour.17 It is never more important for facility managers to adhere to current building ventilation standards and system maintenance. Even so, it is suggested that there is no building ventilation research available that is specific to SARS-CoV-2 transmission.16

As of March 15, 2021, almost 13% of Santa Clara County’s residents have been fully vaccinated for COVID-19.22  Vaccination scheduling is currently open to older adults, those with chronic conditions, and those in certain essential-work positions in the county,23 but vaccine availability in Santa Clara and other counties is strained.24 Moderate exercise enhances immune function25  and may positively impact conditions that are linked to severe COVID-19 disease.26 Though no one suggests exercise will inhibit a COVID-19 infection, exercise may be beneficial in reducing COVID-19 severity.27 One researcher thinks that a super-antioxidant is a factor linking exercise to reduced COVID-19 severity.28 Another paper argues that the effects of exercise on the renin-angiotensin-aldosterone system may be a factor influencing COVID-19 severity.29

Clearly it is important to stay physically active as we make efforts to mitigate viral transmission and disperse vaccines.

So how does this inform opening gym doors to once again pound the treadmill, pump iron, and spin away with your favorite instructor? Is it safe? No amount of precaution removes risk, but If you decide to take advantage of gym access as it begins to open in your area, then it is prudent to make sure your facility is adhering to CDC18 and state10 recommendations such as proper exercise facility ventilation and air filtration standards, adherence to social distancing and recommended limits of participation, and enforcing rigorous equipment cleaning and mask wearing. What can you do? Stay quarantined at home if you have a known exposure or symptoms, disinfect equipment before and after use, keep your distance, and wash your hands. And wear a mask!30


1 Huffington Post. (2021). 7 Heart-Healthy Activities That Have Nothing to Do with Traditional Cardio. Feb 9. Retrieved from

2 Washington Post. (2021). The pandemic’s home-workout revolution may be here to stay. Jan 21. Retrieved from

3 Amar, A., Brach, M., Trabelsi, K., Chtrourou, H., Boukhris O., Masmoudi, L., Bouaziz, B…..& Hoekelmann, A. (2020). Effects of COVID-19 Home Confinement on Eating Behaviour and Physical Activity: Results of the ECLB-COVID19 International Online Survey. Nutrients. 12:1583. doi:10.3390/nu12061583

4 Britannica. (2021). Jack LaLanne. Jan 19. Retrieved from

5 Cooper Aerobics. (n.d.). Aerobics. Retrieved from

6 Jacki’s Aerobic Dancing. (n.d.). About Jacki Sorensen. Retrieved from

7 Jazzercise. (n.d.). About Us. Retrieved from

8 Kodak Digitizing. (n.d.). History of the VHS Tape. Retrieved from

9 California State Government. (2021). Industry Guidance to Reduce Risk. Mar 16. Retrieved from

10 California Department of Public Health & Cal OSHA. (2020). COVID-19 Industry Guidance: Fitness Facilities. Oct 20. Retrieved from–en.pdf

11 Jang, S., Han, S.H., & Rhee, J.Y. (2020). Cluster of Coronavirus Disease Associated with  Fitness Dance Classes,  South Korea. Emerging Infectious Diseases. 26(8):1917-1920.

12 Groves, L.M., Usagawa, L., Elm, J., Low, E., Manuzak, A., Quint, J., Center, K.E., Buff, A.M., & Kemble, S.K. (2021). Community Transmission of SARS-CoV-2 at Three Fitness Facilities — Hawaii, June–July 2020. CDC Morbidity and Mortality Weekly Report. 70(9):316-320.

13 Lendacki, F.R., Teran, R.A., Gretch, S., Fricchione, M.J., & Kerins, J.L. (2021). COVID-19 Outbreak Among Attendees of an Exercise Facility — Chicago, Illinois, August–September 2020. CDC Morbidity and Mortality Weekly Report. 70(9);321–325.

14 Hayashi, M., Yanagi, U., Azuma, K., Kagi, N., Ogata, M., Morimoto, S., Hayama, H., Mori, T., Kikuta, K., Tanabe, S., Kurabuchi, T., Yamada, H., Kobayashi, K., Kim, H., & Kaihara, N. (2020). Measures against COVID-19 concerning Summer Indoor Environment in Japan. Japan Architechtural Review. 3(4):423-434. doi: 10.1002/2475-8876.12183

15 Blocken, B., van Druen, T., Ricci, A., Kang, L., van Hooff, T., Qin, P., Xia, L., Ruiz, C.A., Arts, J.H., Diepens, J.F.L., Maas, G.A., Gillmeier, S.G., Vox, S.B., & Brombacher, A.C. (2021). Ventilation and air cleaning to limit aerosol particle concentrations in a gym during the COVID-19 pandemic. Building and Environment. 193:107659 doi:10.1016/j.buildenv.2021.107659

16 Azuma, K., Yanagi, U., Kagi, N., Kim, H., Ogata, M., & Hayashi, M. (2020). Environmental factors involved in SARSCoV-2 transmission: effect and role of indoor environmental quality in the strategy for COVID-19 infection control.  Environmental Health and Preventive Medicine. 25:66.

17 Blocken, B., van Druen, T., van Hooff, T., Verstappen, P.A., Marchal, T., & Marr, L.C. (2020). Can indoor sports centers be allowed to reopen during the COVID-19 pandemic based on a certificate of equivalence? Building and Environment. 180:107022. doi: 10.1016/j.buildenv.2020.107022

18 CDC. (2021). Guidance for Businesses and Employers Responding to Coronavirus Disease 2019 (COVID-19). Mar 8. Retrieved from

19 ASHRAE. (2020). Guidance for Building Operations During the COVID-19 Pandemic. ASHRAE Journal. 62(5):3

20 Grainger. (2020). What Is MERV Rating? Air Filter Rating Chart. Feb 11. Retrieved from

21 FDA. (2021). UV Lights and Lamps: Ultraviolet-C Radiation, Disinfection, and Coronavirus. Feb 1. Retrieved from

22 Santa Clara County Public Health Department. (2021). COVID-19 Vaccinations Among County Residents Dashboard. Retrieved from

23 Santa Clara County Public Health Department. (2021). COVID-19 Vaccine Information. Retrieved from

24 KTVU. (2021). As eligibility expands, vaccine shortages in California persist. Mar 16. Retrieved from

25 Gentil, P., Barbosa de Lira, C.A., Souza, D., Jimenez, A., Mayo, X., Gryshek, A., Pereira, E.G., Alcaraz, P., Bianco, A., Paoli, A., Papeschi, J., Carnevali Jr, L.C. (2020). Resistance Training Safety during and after the SARS-Cov-2 Outbreak: Practical Recommendations. Bio Med Research International.  2020: 3292916. doi:10.1155/2020/3292916

26Med Page Today. (2020). Exercising in the Fight Against COVID-19. Dec 23. Retrieved from

27University of New Orleans. (2020). Physical Activity Could Reduce Severity of COVID-19 Research Suggests. Jul 30. Retrieved from

28 University of Virginia. (2020). Exercise May Protect Against Deadly COVID-19 Complication, Research Suggests. Apr 15. Retrieved from

29 Evagelista, F.S. (2020). Physical Exercise and the Renin Angiotensin System: Prospects in the COVID-19. Frontiers in Physiology. 11: 561403. doi: 10.3389/fphys.2020.561403

30 Almasri, D., Noor, A., Diri, R. (2020). Behavioral Changes in Gym Attending Due to COVID-19 Pandemic: A Descriptive Survey. J Microsc Ultrastruct. 8(4):165-167. doi: 10.4103/JMAU.JMAU_64_20