Chronic exercise training effects on immune function

MACKINNON. L. T. Chronic exercise training effects on immune function. Med. Sri. Sports Exerc., Vol. 32, No. 7, Suppl., pp. S369-S376. 2000. Purpose: This paper reviews the recent literature on the chronic effects of exercise training. on immune function in humans. There is a general perception by a thletes and other physically active individuals that regular moderate activ ity enhances, whereas intense exercise suppresses, resistance to minor illn esses such as upper respiratory tract infection (URTI). This perception is supported by epidemiological data in endurance athletes and limited data fr om intervention studies using moderate exercise in previously untrained ind ividuals. The apparently high incidence of URTI among endurance athletes ha s prompted interest the relationship between chronic exercise training and immune function. Whereas immune cell number is generally normal during inte nse exercise training, recent evidence suggests that prolonged periods of i ntense training may lead to slight impairment in immune parameters such as neutrophil function, serum and mucosal immunoglobulin levels, plasma glutam ine concentration, and possibly natural killer cell cytotoxic activity. In contrast, moderate exercise training has either no effect on, or may stimul ate, these immune parameters. Conclusion: Whereas athletes are not clinical ly immune deficient, it is possible that the combined effects of small chan ges in several immune parameters may compromise resistance to minor illness es such as URTI. Strategies to prevent URTI in athletes include avoiding ov ertraining, providing adequate rest and recovery during the training cycle and after competition, limiting exposure to sources of infection, ensuring adequate nutrition, and possibly vitamin C supplementation. It is uncertain at present whether moderate exercise training is helpful in preventing inf ectious illness among the wider population.