As we face a global pandemic and focus on staying healthy and safe, the running community has already had over 100 races postponed, cancelled, or moved to virtual with more likely to come (updated sheet of half and full marathon changes from my friend Jim Diego).

I have been asked if running makes us less prone to contract a virus, and if so, shouldn't everyone be running? A free vaccine! On the other hand, many runners can relate to feeling under the weather for a few hours or days after an intensive training block. According to the age-old open window theory, immune system change after prolonged, strenuous exertion makes it easier for viruses and bacteria to gain a foothold and increases the risk of infection. Is this theory a big misconception?

Running strengthens your immune system
Plenty of research supports the health benefits of running. Perhaps the most famous study in 2014 of more than 55,000 adults found that runners had 30% lower risk of all-cause mortality, even at 5 to 10 minutes a day of running. The World Health Organization also has evidence-based Physical Activity Guidelines recommending at least 2.5 hours of moderate-intensity aerobic activity per week.

This naturally makes us wonder, why not run more? Since the 2014 study, additional research has been done with groups of intense runners; one study by Berkeley Lab of more than 156,000 finds that runners logging at least 40 miles a week were 26% less likely to develop coronary heart disease than those running just 13 miles per week. Endurance runners can have wider arteries and more abundant capillaries improving blood circulation. Other psychological research points to greater mental and emotional payoffs from running more.

One of the COVID-19 headlines I came across this week was a Runner's World article on "What Runners Need to Know About Coronavirus". It suggests that runners going through normal training have an enhanced ability to detect and deal with pathogens. But it also claims, like the open window theory, that those who are overtraining or who have just completed a race are more vulnerable to infection because you are "pushing harder than you would in training, causing stress to the immune system."

Does running also suppress your immune system?
When it comes to immune system changes, running causes immune cells to change in two primary ways. Initially when you run, the number of immune cells in the bloodstream increases dramatically with some cells like natural killer cells to fight off infections multiplying by 10x. When you finish a run, immune cells decrease substantially and can remain at low levels for several hours which is often why many claim running "suppresses your immune system."

In fact, contrary to widespread belief, the latest myth-busting research shows that these immune cells are not destroyed but rather move to areas in the body that are likely to become infected like peripheral tissues including the lungs as deeper and faster breathing during aerobic activity increases the chance of inhaling something infectious. In these areas immune cells are believed to identify and eradicate other cells that have become damaged or malignant. In other words, after we run, our immune systems are in a heightened state of surveillance and defense, as opposed to immune suppression.

Although running may not increase the likelihood of catching a virus, other factors might such as training with those who are sneezing or coughing, using gym equipment including treadmill handles, being in places where there is a large gathering of people, and taking public transportation. To minimize COVID-19 and still run, maintain good hygiene and listen to your body. Wash your hands, use antiviral hand gel, avoid touching your eyes, nose, and mouth, don't run with body aches, chest congestion, and/or fever, and don't share water bottles or high-five other runners - an Usain "Lightning Bolt" pose will do.