By Kristen Rogers, CNN

(CNN) -- Now that more people are getting vaccinated against coronavirus, is this the moment to trade your neighborhood cycle for a motivating spin class at the gym?

People can contract or spread coronavirus by exposure to respiratory droplets carrying the virus, virus accumulated in or flowing through the air, or surfaces contaminated with virus. That means "the increased respiratory exertion that occurs in the enclosed spaces of indoor exercise facilities facilitates transmission" of the virus, the US Centers for Disease Control and Prevention has reported.

Infection risk while inside gyms is lower for fully vaccinated people, but unvaccinated people remain unprotected -- so both groups, if they go, should take the same precautions.

No matter what you do, you should stay at least 6 feet away from others and constantly wear a mask that covers your mouth and nose. If the exercise's intensity makes mask wearing difficult, doing that activity outdoors and away from others is especially important, the CDC has advised.

Mask wearing while exercising hasn't been found to be harmful for healthy people, according to the CDC -- but those with a lung disease or heart disease should talk with their health care provider before trying to work out while wearing a mask.

Virtual fitness classes are still available. But if you want to go to the gym, prepare first. Call or look online to check whether the gym is following CDC guidance for gyms, fitness centers and studios. Reserve your spot for a low-usage time and check in online if possible. Learn about practices that may affect your plans, such as closed locker rooms. Even if locker rooms are open, shower at home and arrive in your exercise clothes to avoid being close to others in a small space. Bring two masks in case one gets wet from sweat since, according to the CDC, a wet mask is less effective and can make breathing difficult.

Some gyms "have limited the number of people who can be on the floor," said Dr. Ada Stewart, a family physician with Cooperative Health in Columbia, South Carolina, and the president of the American Academy of Family Physicians. "Most gyms have big windows; they have fans going, so they have a lot of ventilation within there. If you don't see that, then I would try to avoid it if at all possible."

Also keep an eye out for high ceilings, open doors and portable air cleaners that have HEPA (high-efficiency particulate air) filters, which all can help keep spaces well ventilated.

Since risk increases with the level of physical exertion, be choosy about which activities you do. As long as the studio is well ventilated and class size is kept small, low-intensity activities -- such as yoga -- are safer than high-intensity activities including basketball or spinning, which should be done outdoors. Outdoor sessions with guest limits are less risky than indoor group trainings.

High-intensity indoor classes need "to have very good ventilation with people spaced at least 10 feet apart," said CNN Medical Analyst Dr. Leana Wen, an emergency physician and visiting professor of health policy and management at the George Washington University Milken Institute School of Public Health. "If that is not in place, I would look to see whether they are requiring vaccination."

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Before and after you use machines or equipment, use sanitizing wipes to clean them, and sanitize or wash your hands. Don't share equipment that can't be cleaned fast enough between uses by guests, such as weightlifting belts or resistance bands. If you're indoors, "keep your workouts as brief as possible to avoid prolonged exposure," the CDC has suggested.