Human participants research checklist.

<div><p>Background</p><p>The sex difference in athletic performance has been thoroughly investigated in single sport disciplines such as swimming, cycling, and running. In contrast, only small samples of long-distance triathlons, such as the IRONMAN<sup>®</sup> triathlon, have been investigated so far.</p><p>Aim</p><p>The aim of the study was to examine potential sex differences in the three split disciplines by age groups in 5-year intervals in a very large data set of IRONMAN<sup>®</sup> age group triathletes.</p><p>Methods</p><p>Data from 687,696 (553,608 men and 134,088 women) IRONMAN<sup>®</sup> age group triathletes (in 5-year intervals from 18–24 to 75+ years) finishing successfully between 2002 and 2022 an official IRONMAN<sup>®</sup> race worldwide were analyzed. The differences in performance between women and men were determined for each split discipline and for the overall race distance.</p><p>Results</p><p>Most finishers were in the age group 40–44 years. The fastest women were in the age group 25–29 years, and the fastest men were in the age group 30–34 years. For all split disciplines and overall race time, men were always faster than women in all groups. The performance difference between the sexes was more pronounced in cycling compared to swimming and running. From the age group 35–39 years until 60–64 years, the sex differences were nearly identical in swimming and running. For both women and men, the smallest sex difference was least significant in age group 18–24 years for all split disciplines and increased in a U-shaped manner until age group 70–74 years. For age groups 75 years and older, the sex difference decreased in swimming and cycling but increased in running. Considering the different characteristics of the race courses, the smallest performance gaps between men and women were found in river swimming, flat surface cycling and rolling running courses.</p><p>Conclusions</p><p>The sex difference in the IRONMAN<sup>®</sup> triathlon was least significant in age group 18–24 years for all split disciplines and increased in a U-shaped manner until age group 70–74 years. For 75 years and older, the sex difference decreased in swimming and cycling but increased in running.</p></div>