The problem with wearing masks when you exercise outdoors is that they can limit your ability to breathe. This may not be an issue if you are doing casual exercise, but if you are running or cycling vigorously, you will probably find yourself gasping for air. Diana and I do not wear our masks while we are exercising outdoors, but we do not ride close to anyone else. If you are running or riding with other people, space yourselves out to allow at least ten feet between you, and usually quite a bit more. If you exercise somewhere that may be congested, or if you plan to go indoors along your route, use a mask that is easy to move up and down. Let it hang around your neck most of the time, and move it up into position over your nose and mouth when you approach someone else.

Wearing a mask will help to protect others when you cough, sneeze, talk loudly or breathe hard, but they may not protect you. Viruses were shown to pass through cloth masks 97 percent of the time, compared to the special medical masks at only 44 percent of the time. This is what you would expect as the pore size of cloth is far larger than the diameter of a virus. Transmission of a virus through a mask is further increased by moisture retention, reuse of masks and poor filtration (BMJ Open, April 22, 2015;5(4):e006577). Viruses can accumulate on your mask. If you do use a mask, make sure that you wash it after each use. It may be a good idea to change masks every hour or two.

If you are working out in a gym or other indoor space, wearing a mask is an essential courtesy to other people who are using the facility. If you are sharing weight machines or other exercise equipment with anyone, use sanitizing wipes to clean the equipment before and after each use.

Do Not Exercise If You Are Sick
At all times, you should not be near anyone if you are sick or living with someone who is sick. If you have signs of COVID-19 (fever, cough, shortness of breath, chills, shaking, loss of taste or smell, muscle aches, headache, sore throat) or other pending illness, you should not try to exercise. See my report on Exercise with Flu or a Cold?

You Are More Likely to Catch COVID-19 Indoors Than Outdoors
High levels of viruses in the air accumulate indoors in closed spaces, while the air outdoors is constantly circulating to keep concentrations of the virus at much lower levels. A study of 1,245 COVID-19 cases in China found only two were acquired in outdoor environments; 1,243 were acquired in various types of enclosed spaces (MedRxiv, published online April 7, 2020). The authors reviewed 318 outbreaks of more than three people developing COVID-19 in 120 cities. The outbreaks occurred in six location categories: homes, transportation, restaurants, entertainment, shopping, miscellaneous indoor spaces and outdoors. Another study using highly-sensitive laser lights showed that normal speaking emits many thousands of oral fluid droplets per second and they stay in the air for 8 to 14 minutes (PNAS, May 13, 2020).

My Recommendations
Social distancing recommendations apply both indoors or outdoors: stay at least six feet from others when you socialize, eat, shop, attend school and so forth. During exercise, if you are moving fast and breathing hard, the distance should be greater than six feet because you leave a slipstream of virus-carrying droplets from your breath that can extend for ten feet or more behind you.

The FDA has approved dependable antibody tests that are available at local laboratories; check with your health care provider. After people are infected with the coronavirus, their immune system produces antibodies that help to kill the virus now and in the future. We don’t yet have studies to show that people with antibodies in their bloodstream are protected from getting the infection again, or how long that protection will last. However, based on our knowledge of other coronaviruses, the odds are very strong that having antibodies will help to prevent re-infection.