Acute and chronic over-exertion: do depressed immune responses provide useful markers?

There are ethical objections to inducing cumulative muscle damage and associated decrements of performance deliberately in a healthy athlete. Available data on acute and chronic over-exertion thus include the changes of immune response observed following a single bout of exhausting exercise, sequential observations made on top-level competitors as they approach peak training periods, and longitudinal laboratory studies of heavy (but not necessarily damaging) bouts of training. In all three of these situations, subclinical muscle damage initiates an acute inflammatory response, with a resulting deterioration in physical performance. Although much smaller in degree and shorter in duration, the associated changes in immune function are similar to those seen in sepsis. There have been major advances in immunological technique over the past decade, and significant changes in a number of elements of the immune response can be identified in athletes during periods of heavy training. The most promising immunological marker of excessive training seems a decrease in salivary IgA concentration. However, no single change occurs with sufficient consistency to identify the individual competitor who is at risk of overtraining. Mechanisms can be conceived that convert a sequence of excessive training bouts into an acute and then a chronic inflammatory process, but the syndrome of overtraining has a complex overlay of biological and psychological influences. It remains more easily detected by decreases in physical performance and alterations in mood state than by changes in immune function.