It takes a good while for the body to recover from the stress of completing an Ironman. An Austrian study found that blood levels of antioxidant enzymes remained significantly reduced, while biomarkers of muscle damage and inflammation remained significantly elevated in triathletes nearly three weeks after they had crossed an Ironman finish line.
The immune system plays a major role in helping the body recover after exhaustive exercise, but the immune system itself is overwhelmed by the stress of endurance racing and its aftermath. Immune cell function remains depressed for as long as three days after such an experience, greatly increasing the athlete’s susceptibility to viral and bacterial infections. The causes of this effect appear to be multiple and are not fully understood. Part of the problem is that the immune cells’ main fuels, such as the amino acid glutamine, are depleted during exhaustive exercise. It seems that the immune system also downregulates its inflammatory response to tissue damage to avoid out-of-control systemic inflammation that would otherwise result from the high muscle damage incurred. But this very downregulation impairs the immune system’s ability to fight foreign invaders.
Triathletes also commonly suffer from a malady known as the “post-Ironman blues” in the weeks after an Ironman. It is likely that such mood depression is to some degree just another symptom of the general overtraining syndrome that commonly affects endurance athletes after such a test. Overtraining is known to disrupt brain neurotransmitters that influence mood. It has been hypothesized that as a symptom of overtraining, depression is your brain’s way of discouraging you from overexerting yourself again—in this case, doing your next Ironman—for a while.