Isabeau Miller’s FitCamp-August 2008 (Episode 15)

More information that you don’t want to hear, from Rice University:

What is the immune system?

The immune system is a complex, dynamic, and beautifully orchestrated mechanism with enormous responsibility. It defends against foreign invasion by microorganisms, screens out cancer cells, adapts as we grow, and modifies how we interact with our environment. When it malfunctions, disease, cancer or death can occur. Although it is not necessary to understand all the intimate details of the immune system, it is wise to have a basic grasp of its functions. More precisely, we should understand how to stay healthy.

Training the immune system — the “J” curve

It appears that the immune system has a training effect, similar to other areas of physiology (e.g., cardiovascular, muscular). In other words, a balanced training program of exercise and rest leads to better performance. Studies in the laboratory and epidemiological observations have shown improved immune function and fewer URIs (Upper Respiratory Infections) in athletes as compared to their couch-potato counterparts. This is especially true in older athletes and it appears that regular exercise can help attenuate the age related decline in immune function.

On the other hand, too much exercise can lead to a dramatically increased risk of URIs. The stress of strenuous exercise transiently suppresses immune function. This interruption of otherwise vigorous surveillance can provide an “open window” for a variety of infectious diseases — notably viral illnesses — to take hold. This is especially true following single bouts of excessive exercise. For example, it has been observed that two-thirds of participants developed URIs shortly after completing an ultramarathon. Similarly, cumulative overtraining weakens the athlete’s immune system, leading to frequent illness and injury.

The best model that accommodates clinical observations and laboratory experiments is described by the “J”-curve ( Fig. 1). It is important to note that this curve is individualized. What is moderate training for some is overtraining for others.

Stress is cumulative
In addition to strenuous exercise, other forms of stress may also transiently suppress immune function. Since exercise is not the only stress factor, an athlete must consider a host of other variables. There are job responsibilities, family obligations, social interactions, financial concerns and other components that shape our lives. The sum of all of these affects a central axis in the body which ultimately influences immune function. Some of these (e.g., exercise) are under our direct control, and others only partially or not at all. Recognizing when excess stress occurs is easier if it just comes from one source. However, all too often it is the sum of many small, difficult to recognize changes that tips the scales and sends the athlete into the whirlpool of overtraining and immunosuppression. Alone and in isolation these small changes would be manageable, but combined they can overwhelm. (Fig. 2.)