Are indoor workouts COVID safe? Nearly 70% of people in one class got sick, CDC says

New reports from the Centers for Disease Control and Prevention have some worrying findings for people itching to go back to the gym amid the coronavirus pandemic — especially if proper precautions to slow transmission aren’t taken.

Data on coronavirus spread within gyms and other exercise facilities are limited, experts say, but there have been a handful of outbreaks that suggest heavy breathing, shouting instructors and infrequent mask wearing, among other culprits, play major roles in viral transmission.

Two gyms in Hawaii and Illinois, where attendees went to fitness classes right before and even after coronavirus symptoms began, are at the heart of the CDC’s latest push for stricter precautions in exercise facilities.

The case reports published Wednesday by the health agency detail what infection precautions were in place and which ones were not, revealing what’s been working and reinforcing how important certain measures are in slowing coronavirus spread.

The agency says staff members and gymgoers should wear properly worn masks, including during high-intensity activities, physically distance from others — and stay home if they are sick, believe they are infected or are awaiting their test results.

Better yet, people should exercise outdoors or virtually, the CDC says, as risks of coronavirus infection are further reduced.

However, during last summer in Chicago, staff and attendees did the opposite. Researchers detected 55 COVID-19 cases among an 81-person high-intensity fitness class held indoors in just one week — 68% of the group.

Most attendees said they wore masks infrequently (76%), including 84% of those who ended up testing positive for coronavirus and 60% of those who didn’t, according to the CDC report.

The problematic cherry on top: 22 people (40%) attended the fitness class on or after their coronavirus symptoms began.

Overall, 43 (78%) attendees participated in multiple classes while potentially contagious with coronavirus.

“In Chicago, you had members who went to class when they were symptomatic or Covid-positive,” Alex Larcom, International Health Racquet and Sportsclub Association senior manager of health promotion and health policy, told the New York Times.

“We are relying on people who are sick or think they are sick to remove themselves from society,” Larcom told the outlet. She added that the people who went to the gym despite feeling symptoms “were probably also going to the grocery store, going out to eat and moving through the community.”

The Chicago Department of Public Health blamed the outbreak on the large number of people who took the class while symptomatic or asymptomatic. The CDC adds that infrequent mask wearing and aerosolized transmission — when virus particles enveloped in respiratory droplets emitted during heavy breathing, shouting or coughing travel in the air — may have played a role.

What’s more, the Chicago gym was not originally designed for exercise classes, the CDC said, meaning “inadequate air circulation” could have also led to coronavirus spread, although this was not assessed.

A similar, but smaller, outbreak occurred in a gym in Honolulu, Hawaii, where 21 COVID-19 cases were linked to a 37-year-old fitness instructor, who infected another instructor and taught classes at several gyms in the days leading up to coronavirus symptom onset.

Just four hours before his symptoms began, the instructor taught a stationary cycling class indoors with 10 attendees — they all tested positive days later.

The second instructor to test positive taught five personal training and small-group kickboxing sessions with 10 participants just two days after his first exposure to the coronavirus. He was later hospitalized and admitted to an intensive care unit along with one other attendee.

Masks were not worn or required in the Honolulu gym at the time.

The CDC says this COVID-19 cluster happened even when Hawaii community transmission of the virus was low, and despite workout machines being separated by six feet. The instructors’ shouting during workouts and aerosol emission during loud speech might have also played roles, experts said.

The report adds that “the rate of transmission was highest on the day of symptom onset for both instructors,” which is consistent with what other studies have found.

Still, the true number of people who became infected with the coronavirus in both the Chicago and Honolulu events may have been underestimated because asymptomatic individuals may not have been tested.