Something has gone wrong. Lately it seems that you have been sick a lot. You feel listless at home, bored at work, and your workouts have been lousy. Getting motivated for anything takes supreme willpower. When yet another upper respiratory infection hits, you decide to lay off the exercise and stew in the juices of frustration. What has happened?
If this scenario sounds familiar the you're not alone. Frequent upper respiratory infections (URIs) are just one of the signs that your body is being pushed too hard. Coaches have observed that some athletes appear to be frequently ill and, historically, in both the summer and winter Olympic games, team physicians have noted the common occurrence of URIs. All too often this tarnishes the athletes chance at gold.
An opposing perspective comes from athletes, most of whom believe that they are healthier since starting an exercise program. Furthermore, most medical authorities tell us that exercise promotes good health. Why do some athletes get sick frequently while others remain healthy? Is exercise good or bad for the immune system?
The goal of this article is to review the current understanding of the athlete's immune system, and hopefully, teach you how to use this knowledge to stay healthy. First, a few points about viral URIs. They are not caused by getting cold or wet. They are caused by viruses. Person-to-person transmission by aerosolized droplets or direct contact is how these viruses can spread. Antibiotics are not useful in treating viral URIs. Finally, any given viral URI may behave differently in different people. This is because each persons immune system is unique.
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.
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 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.
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.)
Currently, the best way to stay healthy is to listen to your body. Recognizing the early warning signs and adapting the training schedule accordingly can help keep you healthy. In that light, here are some points to ponder and a few recommendations,