Immune responses and increased training of the elite athlete.

Ten elite male runners (age, 29.8 +/- 1.7 yr; maximum oxygen consumption, 65.3 +/- 4.9 ml.kg-1.min-1; 10-km times, 31 min 43 s +/- 1 min 46 s) deliberately increased training schedules by an average of 38% for 3 wk. Resting heart rate and maximal oxygen intake were unchanged, but the heart rate response to acute exercise was decreased. Following heavy training, blood samples taken at rest showed trends to a decreased helper/suppressor cell ratio, an increased phytohemagglutinin (PHA)- and concanavalin (ConA)-stimulated lymphocyte proliferation, and a decreased production of immunoglobulins IgG and IgM. Whereas PHA-stimulated lymphocyte proliferation was initially unchanged by acute exercise, after 3 wk of heavy training the same acute exercise caused an 18% suppression of proliferation. Acute exercise following heavy training did not alter pokeweed-stimulated IgG or IgM synthesis. There was no correlation between changes in lymphocyte subpopulations, helper/suppressor ratios, and mitogen-induced cellular proliferation. The immune system of endurance-trained athletes at rest seemed to tolerate the stress of heavy training, but superimposition of a bout of acute exercise on the chronic stress of heavy training resulted in immunosuppression, which was transient and most likely not of clinical significance.