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By studying this chapter, you should be able to do the following:

  1. Describe how the innate and acquired immune systems work together to protect against infection.

  2. Discuss the key components that make up the innate immune system, and describe how the major elements of the innate immune system protect the body against infection.

  3. Outline the primary components that compose the acquired immune system and explain how they protect against infection.

  4. Explain the differences between acute and chronic inflammation.

  5. Discuss the effects of moderate exercise training on the immune system and the risk of infection.

  6. Explain how an acute bout of intense and prolonged (>90 minutes) exercise impacts immune function and the risk of infection.

  7. Discuss how exercise in environmental extremes (heat, cold, and high altitude) influence immune function.

  8. Explain the guidelines for exercise when you have a cold.


Overview of the Immune System

  • Innate Immune System

  • Acquired Immune System

Exercise and the Immune System

  • Exercise and Resistance to Infection

  • Exercise, Circulating Immune Cell Counts, and Activity

  • High-Intensity/Long-Duration Aerobic Exercise Increases the Risk of Infection

Exercising in Environmental Extremes: Increased Risk for Infection?

Should You Exercise When You Have a Cold?

Key Terms


cell adhesion molecules

complement system


exercise immunology








natural killer cells




The concept of homeostasis and the control systems that regulate the internal environment were introduced in Chap. 2. The immune system is a critical homeostatic system that recognizes and destroys foreign agents in the body. Obviously, this is important because the body is constantly under attack from foreign agents (e.g., bacteria, viruses, and fungi) that promote infection. That all mammals and higher organisms have an immune system highlights the fact that periodic infection is a biological reality. Accordingly, the immune system plays an important role in maintaining homeostasis. As a fundamental concept, a properly functioning immune system is able to protect the body because it is able to discern self from nonself (foreign agents).

Everyone has experienced an infection and the effects of the immune system. The unpleasant symptoms (i.e., runny nose and fever) of an upper respiratory tract infection (URTI), for example, are common place. URTIs are commonly referred to as colds and are caused by more than 200 different viruses (20). Currently, URTIs are the most common types of infections worldwide, and the average adult suffers from two to five colds a year (14, 29). Although colds are not usually life threatening in healthy individuals, colds have many negative consequences because of increased healthcare costs and lost days from work, school, and exercise training (16). Because of the high occurrence of colds, these illnesses present a real concern to the health of athletes and the general population. Since exercise and other stresses (e.g., emotional stress, loss of sleep, etc.) are known to influence the ...

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