An ironman triathlon does not lead to a change in body mass in female triathletes.

In 16 female nonprofessional Ironman triathletes, body mass, percent body fat, and skeletal muscle mass were determined before and after an Ironman race in order to detect changes. Selected hematological and urinary variables as well as percent total body water were measured in order to quantify a change in hydration status. Body mass, skeletal muscle mass, percent body fat, and percent body water did not change (p > 0.05). Plasma volume increased significantly by 8.1 (13.7) % (p < 0.05). The significant increase in plasma volume, plasma urea concentration, and urinary specific gravity after the race was associated with a significant fall in hematocrit and plasma sodium concentration (p < 0.05). In contrast to studies of male Ironman triathletes, we could not detect a decrease in body mass in female Ironman triathletes. The statistically insignificant loss of 0.6 kg in body mass was smaller than reported in studies of male athletes.