title: Changes in body composition in triathletes during an Ironman race.
abstract: OBJECTIVE
  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 ± 0.8 kg. This loss was due to 0.4 ± 0.3 and 1.4 ± 0.8 kg 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 < 0.01).
  
  
  CONCLUSIONS
  The loss in lean mass was explained by a decrease in muscle density, as an indicator of glycogen loss, and increases in several indicators for dehydration. The measurement of body composition with DXA and pQCT before and after an Ironman triathlon provided exact values for the loss in fat and lean mass. Consequently, these results yielded more detailed insights into tissue catabolism during ultra-endurance exercise.
authors.affiliation: Exercise Physiology, Institute of Human Movement Sciences, ETH Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors.forename: Sandro Manuel
authors.initials: SM
authors.lastname: Mueller
authors.forename: Elmar
authors.initials: E
authors.lastname: Anliker
authors.forename: Patrizia
authors.initials: P
authors.lastname: Knechtle
authors.forename: Beat
authors.initials: B
authors.lastname: Knechtle
authors.forename: Marco
authors.initials: M
authors.lastname: Toigo
mesh_terms: D000328:Adult; D056352:Athletes; D001642:Bicycling / Q000502:physiology*; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D002149:Energy Intake / Q000502:physiology; D005223:Fats / Q000378:metabolism; D006400:Hematocrit / Q000379:methods; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D009994:Osmolar Concentration; D011188:Potassium / Q000097:blood; D012420:Running / Q000502:physiology*; D012964:Sodium / Q000097:blood; D013550:Swimming / Q000502:physiology*
chemical_list: D005223:Fats; D006454:Hemoglobins; D012964:Sodium; D011188:Potassium