The WHO says masks shouldn't be worn during intense physical activity, contradicting other advice

• Masks do not need to be worn during "vigorous intensity physical activity," the World Health Organization said in updated guidelines, citing some research that wearing them can have negative effects.
• The organization said other prevention measures, like distancing and ventilation, need to be in place in indoor exercise venues, or they should temporarily close.
• Some experts disagree with the guidance, however, citing research showing that masks don't impair breathing and that the WHO-recommended 1-meter of distance isn't enough.
• In other areas, the updated guidelines tighten mask-wearing advice, suggesting the general public wear them indoors, with some exceptions.

Masks should not be worn during "vigorous intensity physical activity," according to controversial guidance the World Health Organization released Tuesday.

The advice doesn't appear to be entirely new for the organization, though it surprised experts and contracts some research.

The WHO said the updated guidelines, which include tightened mask-wearing advice in situations other than exercise, are based on the latest research, though more is needed. Masks, it reiterated, aren't a silver bullet but need to be used as a part of a comprehensive plan to defeat the novel coronavirus.

You don't need to wear a mask to the gym, the WHO said, but ventilation and distancing are key

There's not a lot of research on the pros and cons of wearing masks during exercise. But the WHO pointed out that some studies have shown wearing them during mild to moderate physical activity can lead to significant negative cardiovascular and pulmonary effects in both healthy people and those with underlying respiratory diseases.

People who wear respirators while exercising, as well as those who have diseases like asthma and COPD and wear any mask while working out, seem to fare worst.

As such, WHO said "people should not wear masks during vigorous intensity physical activity because masks may reduce the ability to breathe comfortably." On the "mythbusters" section of its website,the organization adds "sweat can make the mask become wet more quickly which makes it difficult to breathe and promotes the growth of microorganisms."

The organization says in the new report that good ventilation and physical distancing of at least three feet during workouts is paramount. If gyms can't guarantee distancing, ventilation, and proper disinfection, they should consider closing temporarily, the WHO said.

The advice contradicts other research and expert input

A gym in Virginia exemplifies how aspects of WHO's strategy can work. The facility worked with member Dr. Linsey Marr, an airborne viral transmission expert, to ensure stellar ventilation, which included opening all its warehouse doors. They also distanced exercisers and didn't require masks.

When one trainer became infected with COVID-19, theoretically exposing 50 gym-goers, none got sick.

But one of the reasons the gym is a success story is likely its distance between exercisers: 10 feet, as opposed to the WHO's recommended three.

When people are breathing heavily, expelling potentially contagious particles into the air, even six feet might not be safe, Marr previously told Insider's Gabby Landsverk.

"It's likely that higher intensity exercise is riskier because people produce more aerosols when they're breathing faster and harder," Marr said. She recommended trying to visit the gym when it's least crowded and to wear a mask if it doesn't seem to have good ventilation.

Another expert, Dr. Megan Ranney, an emergency-medicine physician at Brown University, told Insider the WHO's new guidance is "terrifying."

"That just makes no sense," she said. "There have been studies showing that face masks don't actually inhibit breathing or [oxygen levels] during exercise." One small study, for instance, showed that healthy exercisers' blood and muscle oxygen levels weren't affected when performing the same fitness test with a cloth mask, medical mask, and no mask.

"Our findings are of importance because they indicate that people can wear face masks during intense exercise with no detrimental effects on performance and minimal impact on blood and muscle oxygenation," the researchers wrote in a press release.

Meantime, some jurisdictions in the US have mandated masks in gyms, and many gym chains have done the same.

The WHO tightened its mask-wearing guidance in other areas

In non-exercise situations, the WHO tightened its stance on masks.

In healthcare settings in areas with community transmission, everyone should wear them, including outpatients and visitors, the WHO said. Inpatients should wear them when leaving their area or when physical distance can't be maintained.

The organization still recommends that healthcare workers caring for COVID-19 patients wear N95-type masks when performing procedures that could generate aerosols. They should wear medical masks otherwise.

In places with "known or sporadic" transmission, healthcare workers should wear medical masks when patients are present, the WHO said. The organization also said healthcare workers shouldn't wear respirators with valves, since those allow exhaled air to bypass the filtration system.

The WHO said the general public should also wear non-medical masks both inside public places and outside when physical distancing isn't possible. Even if it is possible indoors, masks should be worn unless there's sufficient ventilation.

If you're having visitors, WHO said wear a mask if you can't maintain distance or ensure good ventilation.

WHO also recommended people at higher risk for serious COVID-19 complications, like those over 60 and those with conditions like heart disease, chronic lung disease, or cancer, wear medical masks when they can't maintain physical distance. Caregivers or housemates of suspected or confirmed COVID-19 should also wear medical masks when in the same room.

Kids over 12 should follow adult mask-wearing guidance

WHO also addressed mask-wearing in kids, saying that kids over 12 should follow the same advice given to adults. Younger kids should wear a mask on a more case-by-case basis, taking into consideration factors like whether they live with vulnerable people or are able to wear one appropriately.

Kids 5 and younger don't need to wear masks as "source control," or in an effort to block COVID-19 transmission at its source, WHO said. Evidence suggests young kids' risks of spreading the virus to other kids and adults is low.

Finally, the updated guidance touches on the best homemade mask materials: An inner layer that absorbs, and middle and outer layers that repel moisture. The WHO discourages masks with valves.

Business Insider Senior Science Reporter Aria Bendix contributed to the reporting of this story.