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Immune System, Exercise and

The interaction between the immune system and exercise is complex and not completely understood. As the body's defense mechanism against infection, the immune system plays an integral role on a daily basis in keeping both athletes and the general population healthy. Exercise can affect the immune system either favorably or unfavorably depending on the type, intensity, and duration of the activity. It is widely accepted that upper respiratory tract infections (URTIs) are a major reason for poor performance in competitive athletics. Many of these athletes have been training at a high level in the preceding weeks, which may contribute to the lowering of their body's resistance to infection. Recreational athletes may also suffer from URTIs following episodes of heavy or unaccustomed exercise bouts. Understanding the impact of exercise on the immune system and its role in health maintenance will ultimately lead to better sports and work performance.

The Immune System: Innate and Adaptive

A full appreciation of the complex interactions between the environment, training, infection, and the immune system requires an understanding of the basics of immune system function. The immune system is made up of two complementary defenses—the innate immune system and the adaptive immune system. The innate system is a collection of mechanisms that are the body's first-line defense against potential pathogens, or infection-causing agents. These include the skin and the mucous membranes, which are physical boundaries against invasion. However, not all portals of entry into the human body are protected by the skin. These sites, including the nasal passages and oropharynx, are equipped with special mucus, enzymes, and complex proteins that immediately start the breakdown process of unwanted pathogens. The innate system begins the process of activating the inflammatory response, which is an important sequence of events leading to the four classic signs of inflammation: rubor (redness), calor (heat), tumor (edema), and dolor (pain).

While the innate immune system is predictable and mechanical, the adaptive immune system is more involved and complex. This is largely due to the mechanisms that allow it to remember specific pathogens and subsequent inflammatory responses. Having “memory” enables the adaptive system to recognize a certain pathogen that it has already been exposed to and quickly mount an immune response on reexposure. This process is carried out through three mechanisms. The first entails recognizing specific proteins on cell surfaces, called antigenic markers, that signify specific pathogens. After recognition, the adaptive system is capable of a cellular and molecular attack against that specific pathogen. Finally, with subsequent repeat attacks from those same pathogens and their associated cell surface proteins, the body's memory system can mount an accelerated response to ensure a balanced immune response and maintenance of health.

Exercise and Immune System Function

The impact of exercise and training on the immune system has been a topic of great interest over the past couple of decades. Many of the currently accepted principles have been developed over this time period. Research is certainly ongoing and evolving in this relatively new field of sports immunology. As exercise grows as a cornerstone of health promotion and disease prevention, it is increasingly important to understand the interaction of exercise and the immune system. Furthermore, as URTIs are appreciated as a contributing factor to poor sports performance, as well as a frequent cause of absenteeism in the work-place, more research is necessary.

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