How does excessive training affect the immune system?

Excessive training can lead to a temporary suppression of the immune system due to a variety of physiological stressors associated with high-volume or high-intensity exercise. During periods of intense training, the body experiences elevated levels of stress hormones like cortisol, which can inhibit the function of immune cells. This suppression can increase vulnerability to infections, as the body's ability to respond to pathogens may become compromised.

Moreover, the immune system is complex and requires a balance; while moderate exercise is known to enhance immune function, excessive exercise without adequate recovery can lead to fatigue and increased risk of illness. The concept of the "open window" theory supports this, suggesting that after intense training sessions, there's a period during which the immune system is less effective.

Thus, the impact of excessive training on the immune system underscores the importance of moderation, recovery, and overall balance in exercise regimens to maintain optimal health and immune function.