It is commonly believed that some forms of exercise, such as endurance events, suppress your immune system and leave you at risk of infections, like the common cold. However, our latest review of the evidence suggests that this is probably not true. In fact, exercise seems to boost the immune system.
The idea that endurance exercise suppresses the immune system stems from research in the 1980s and 1990s. In these studies, competitors of endurance running events, such as the Los Angeles Marathon, were asked if they had symptoms of infections in the days and weeks after the race. Many did, leading to the idea that endurance exercise increases infection risk.