There are no published data on the reliability (reproducibility) of competitive performance, even though it has a profound effect on an athlete's medal prospects and on the ability of sport scientists to identify factors that affect medal prospects. I have therefore analyzed the reliability of elite track-and-field athletes in a series of international competitions. I obtained official results of events in the 17 competitions of the 1997 Grand Prix series at the website of the International Amateur Athletic Federation. I analyzed an event only if at least five athletes each entered the event in two or more competitions. My measure of reliability was the typical within-athlete variation, derived as a coefficient of variation by two-way analysis of variance of log-transformed times (for running and hurdling ev ents) or distances (for jumping and throwing events). I grouped events with similar reliabilities. Results: (a) Within-athlete variations were as follows: running and hurdling events up to 1500 m, 1.0% (95% likely range 0.9 to 1.2%); longer runs and steeplechase, 1.4% (1.3 to 1.5%); triple and high jump, 1.7% (1.5 to 2.0%); pole vault and long jump, 2.4% (2.1 to 2.7%); discus, javelin, and shot put, 2.8% (2.5 to 3.3%). (b) Men and women had similar reliabilities in events where comparable data were available. (c) There was no apparent effect of time between competitions (2-101 days) on reliability, as evidenced by plots of within-athlete variation for all possible pairs of competitions against time between the competitions. (d) The top-half athletes in each event were almost always more reliable than the bottom-half: running and hurdling up to 1500 m, 0.8 vs 1.1%; longer runs and steeplechase, 1.1 vs 1.6%; triple and high jump, 1.7 vs 1.9%; pole vault and long jump, 2.3 vs 2.1%; discus, javelin, and shot put, 2.5 vs 3.3%. Conclusions: (a) The higher reliability of the shorter running and hurdling events may be due to differing contributions of energy systems, pacing strategies, and wind resistance relative to the longer events. Contributions of energy systems and skill may explain the lower reliability of the field events and differences between the field events. (b) Elite female track-and-field athletes reproduce their performances with the same precision as their male counterparts. (c) Elite track-and-field athletes hold their form consistently for at least three months. (d) Bottom-half athletes probably vary their effort more than top-half athletes when a medal is unlikely. (e) Recent work has shown that the smallest worthwhile performance enhancement is about half the within-athlete variation between competitive events, so coaches and sport scientists should focus on enhancements of as little as 0.4-0.6% for elite track athletes through 0.9-1.2% for elite field athletes.
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