Most people assume exercise makes you more likely to catch a cold, not less. That belief mostly comes from watching elite marathoners get sick after races. For everyday recreational sports, the opposite is closer to the truth. During a game, your body pumps immune cells, natural killer cells and neutrophils, into your bloodstream at higher rates. These cells patrol for threats, and regular players get this patrol boost several times a week. Over months, that adds up to a more responsive system. Why