Objectives: The aim of this study was to analyze the impact of body shape and body composition on Ironman performance. It was also aimed to give Ironman trainers and coaches a useful and reliable tool to evaluate performance level and physical improvements in the training process.

Methods: A total of 119 male and 17 female competitors of the Ironman Switzerland volunteered in this study. Ten anthropometric dimensions were measured and a Bioelectrical Impedance Analysis (BIA) was done for all subjects. The obtained variables were compared with race performance.

Results: The somatotype (body shape) was a strong predictor of Ironman performance (R = .535; p < 0.01) in male athletes. An ideal somatotype of 1.7 - 4.7 - 3.1 could be established. Body composition hat only a small impact on race performance (R = .255; p < 0.01). A combination of variables in body shape and body composition can explain for 30.7 % the variance in Ironman performance in male athletes. In female athletes no correlations between body shape, body composition and race performance were found. Body height was the only variable correlating with race time (r = - .590; p < 0.05).

Conclusions: Body shape is a better predictor than body composition in male Ironman performance. By measuring five anthropometric variables, 28.7 % of the variance in race performance can be predicted. These measurements as well as the ideal somatotype can be used by trainers and coaches to control the training process and the physical improvements of their male Ironman athletes.