European Journal of Applied Physiology

, Volume 113, Issue 9, pp 2343–2352

Changes in body composition in triathletes during an Ironman race

  • Sandro Manuel Mueller
  • Elmar Anliker
  • Patrizia Knechtle
  • Beat Knechtle
  • Marco Toigo
Original Article

DOI: 10.1007/s00421-013-2670-3

Cite this article as:
Mueller, S.M., Anliker, E., Knechtle, P. et al. Eur J Appl Physiol (2013) 113: 2343. doi:10.1007/s00421-013-2670-3



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).


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.


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).


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.


Dual-energy X-ray absorptiometry (DXA)Peripheral quantitative computed tomography (pQCT)GlycogenDehydration



Total muscle cross-sectional area


Total fat cross-sectional area


Bioelectrical impedance analysis


Dual-energy X-ray absorptiometry


Muscle protein breakdown


Muscle protein synthesis


Peripheral quantitative computed tomography


Region of interest


Standard deviation


Volumetric bone mineral content

Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Sandro Manuel Mueller
    • 1
  • Elmar Anliker
    • 1
  • Patrizia Knechtle
    • 2
  • Beat Knechtle
    • 2
  • Marco Toigo
    • 1
    • 3
    • 4
  1. 1.Exercise PhysiologyInstitute of Human Movement Sciences, ETH ZurichZurichSwitzerland
  2. 2.Institute of General Practice and Health Services ResearchUniversity of ZurichZurichSwitzerland
  3. 3.Institute of PhysiologyUniversity of ZurichZurichSwitzerland
  4. 4.Zurich Center for Integrative Human PhysiologyUniversity of ZurichZurichSwitzerland