"The physique of Ironman triathletes was considered to be similar to that of cyclists. We intended to investigate differences and similarities in anthropometry and training between 83 Ironman triathletes competing in a qualifier for 'Ironman Hawaii' and 84 ultra-endurance cyclists competing in a qualifier for the 'Race across America'. The anthropometric and training characteristics were compared between these two groups of athletes; associations of anthropometric and training characteristics with race time were investigated using bi- and multi-variate analysis. The Ironman triathletes had shorter legs, lower circumferences of upper arm, thigh and calf and a lower skeletal muscle mass compared to the ultra- cyclists. The Ironman triathletes invested more weekly training hours but fewer weekly cycling hours than the ultra-cyclists; the ultra-cyclists completed more cycling kilometres per week. In the multi- variate analysis, the skin-fold thicknesses at abdominal (P = 0.02) and iliacal site (P = 0.02) as well as percent body fat (P = 0.0008) were associated with race time for the Ironman triathletes. The abdominal (P = 0.003) and the iliacal (P = 0.02) skin-fold thicknesses, percent body fat (P = 0.001) and cycling speed during training (P = 0.01) were related to cycling split time in the Ironman race. For the ultra-cyclists, percent body fat (P = 0.04) was related to race time. We concluded that anthropometry and training of Ironman triathletes were different when compared to ultra-endurance cyclists."