Does exercise help or hinder our bodies’ ability to fight off infections?

In the context of the novel coronavirus outbreak, that question has gained urgency and also, thanks to recent research, emergent answers. The latest science suggests that being fit boosts our immune systems, and that even a single workout can amplify and improve our ability to fight off germs.

But some studies also indicate that the types and amount of exercise may influence how exercise affects our immune responses. More is not necessarily better. And the location of the exercise could matter, too; cue recent findings about the germiness of gyms.

What follows is an overview of the state of today’s science about how and why exercise interacts with our immune systems and whether we should plan to remain active, even as the incidence of new virus cases continues to grow.

Many of us who exercise have heard from well-meaning friends, spouses or parents that strenuous exercise will tamp down our immune systems, opening us to pathogens and illness. That notion gained credence in the late 1980s, the result of studies showing that “marathon running increased the incidence of infection symptoms among runners in the days and weeks after the race,” says John Campbell, a professor of health science at the University of Bath in England and co-author of an influential 2018 review of exercise and immunity.