Immune dysfunction can be a major source of decreased performance in athletes. It currently appears that the effects of exercise on inflammatory and immune responses are hormetic in nature, meaning that moderate exercise is beneficial, whereas chronic intense exercise can be detrimental. Extreme chronic exercise can lead to immunodepression and possibly symptoms of overtraining. because many athletes train at extreme volumes and/or intensities, an understanding by the athletes and coaches of basic theories of immunode-pression is important in ensuring quality training. Copyright © Lippincott Williams & Wilkins.