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Changes in body composition in triathletes during an Ironman race

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Abstract

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 ± 0.8 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.

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Abbreviations

Ar.muscle:

Total muscle cross-sectional area

Ar.fat:

Total fat cross-sectional area

BIA:

Bioelectrical impedance analysis

DXA:

Dual-energy X-ray absorptiometry

MPB:

Muscle protein breakdown

MPS:

Muscle protein synthesis

pQCT:

Peripheral quantitative computed tomography

ROI:

Region of interest

SD:

Standard deviation

vBMC:

Volumetric bone mineral content

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Acknowledgments

The authors thank Andrea Wirth, Birte Ellenrieder, Claudia Mrazek, Jolanda Bürge and Christoph Villiger for the technical assistance during the race.

Conflict of interest

The authors declare that they have no conflict of interest.

Author information

Authors and Affiliations

  1. Exercise Physiology, Institute of Human Movement Sciences, ETH Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland

    Sandro Manuel Mueller, Elmar Anliker & Marco Toigo

  2. Institute of General Practice and Health Services Research, University of Zurich, Zurich, Switzerland

    Patrizia Knechtle & Beat Knechtle

  3. Institute of Physiology, University of Zurich, Zurich, Switzerland

    Marco Toigo

  4. Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland

    Marco Toigo

Authors
  1. Sandro Manuel Mueller
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  2. Elmar Anliker
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  3. Patrizia Knechtle
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  4. Beat Knechtle
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  5. Marco Toigo
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Corresponding author

Correspondence to Marco Toigo.

Additional information

Communicated by Jean-René Lacour.

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Mueller, S.M., Anliker, E., Knechtle, P. et al. Changes in body composition in triathletes during an Ironman race. Eur J Appl Physiol 113, 2343–2352 (2013). https://doi.org/10.1007/s00421-013-2670-3

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  • DOI: https://doi.org/10.1007/s00421-013-2670-3

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