Changes in body composition in triathletes during an Ironman race

Purpose: Triathletes lose body mass during an Ironman triathlon. However, the associated body composition changes remain enigmatic. Thus, the purpose of this study was to investigate Ironman-induced changes in segmental body composition, using for the first time dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Methods: Before and after an Ironman triathlon, segmental body composition and lower leg tissue mass, areas and densities were assessed using DXA and pQCT, respectively, in eight non-professional male triathletes. In addition, blood and urine samples were collected for the determination of hydration status. Results: Body mass decreased by 1.9±0.8kg. This loss was due to 0.4±0.3 and 1.4±0.8kg decrease in fat and lean mass, respectively (P<0.01). Calf muscle density was reduced by 1.93±1.04% (P<0.01). Hemoglobin, hematocrit, and plasma [K+] remained unchanged, while plasma [Na+] (P<0.05), urine specific gravity and plasma and urine osmolality increased (P