Characterising the individual performance responses to mild illness in international swimmers

Objectives: To determine individual differences in the impact of illness on the change in performance of swimmers in international competitions. Methods: Subjects were members of the Australian swimming team ( 33 male and 39 female, aged 15 - 27 years). Swimmers provided a weekly seven day recall of symptoms of illness during final six weeks of preparations for international competition over a three year period. Swimmers were categorised as either ill ( one or more episodes of illness) or healthy. The measure of performances was the international point score. Mean changes in points score were calculated for healthy and ill swimmers between a national championship and an international competition (similar to 16 weeks later). Likelihoods of substantial effects of illness on an individual's true change in performance (beneficial/trivial/harmful) were estimated from means and standard deviations, assuming a smallest substantial change of 6 points. Results: Illness was reported before international performances by 38% of female and 35% of male swimmers. For female swimmers the change in performance was -3.7 (21.5) points ( mean (SD)) with illness and -2.6 (19.0) points when healthy; for male swimmers the changes were -1.4 (17.5) points with illness and 5.6 (13.2) points when healthy. The likelihoods that illness had a substantial beneficial/trivial/ harmful effect on performance of an individual swimmer were 32%/31%/37% for female and 17%/31%/ 52% for male participants (90% confidence limits similar to +/- 10% to 20%). Conclusions: Although mild illness had only a trivial mean effect on female swimmers and a small harmful mean effect on male swimmers, there were substantial chances of benefit and harm for individuals.