Open-Window Effect: Is your immune system more vulnerable after training?
Scientists have long suspected that elite endurance athletes are more prone to upper respiratory infections. A striking pattern has emerged: acute infections often occur after intense exertion, demanding training phases, or competitions. One possible explanation for this phenomenon is the Open-Window Effect.
Exhausted and happy at the finish line of the BMW BERLIN-MARATHON 2024. © SCC EVENTS/Tilo Wiedensohler
What’s Behind It?
The Open-Window Effect is a scientific hypothesis that has yet to be definitively proven. It describes a timeframe of up to 24 hours after intense physical exertion in which the immune system is temporarily weakened. A stressed mucosal epithelium in the upper respiratory tract can impair the body's first line of defense—making it easier for pathogens to enter.
Additionally, immune cell levels fluctuate: during exercise, the number of lymphocytes increases in proportion to the intensity and duration of the workout. However, in the initial hours of recovery, their levels drop below baseline before stabilizing again within 24 hours. Besides exercise, factors like sleep, nutrition, and psychological stress also impact immune function.
These two participants protect themselves with the reusable poncho at the finish line. © SCC EVENTS /Tilo Wiedensohler
How Can You Protect Yourself?
To stay healthy, make sure to change into dry clothes quickly after training, get enough sleep, and manage stress effectively. This helps strengthen your immune defenses! And if you do catch a cold, don’t worry—adults typically experience four to five mild infections per year. The good news: endurance training boosts your immune system, but proper recovery is an essential part of the process.
