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Do ultra-runners in a 24-h run really dehydrate?

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Abstract

Background

Loss of body mass during a 24-h run was considered to be a result of dehydration.

Aims

We intended to quantify the decrease in body mass as a loss in fat mass or skeletal muscle mass and to quantify the change in hydration status.

Methods

Body mass, fat mass, skeletal muscle mass, haematocrit, plasma sodium and urinary specific gravity were measured in 15 ultra-marathoners in a 24-h run.

Results

Body mass decreased by 2.2 kg (p = 0.0009) and fat mass decreased by 0.5 kg (p = 0.0084). The decrease in body mass correlated to the decrease in fat mass (r = 0.72, p = 0.0024). Urinary specific gravity increased from 1.012 to 1.022 g/mL (p = 0.0005).

Conclusions

The decrease in body mass and the increase in urinary specific gravity indicate dehydration. The decrease in body mass was correlated to the decrease in fat mass and therefore not only due to dehydration.

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Acknowledgments

We thank the crew of ‘Sri Chinmoy Marathon Team Switzerland’ for their generous support and the athletes for their promptitude to collect data during the race. For their help in translation, we thank Matthias Knechtle, Lausanne, Switzerland, and Mary Miller from Stockton-on-Tees, Cleveland in England, crew member of an ultra-endurance support crew.

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Authors and Affiliations

  1. Gesundheitszentrum St. Gallen, Vadianstrasse 26, 9001, St. Gallen, Switzerland

    B. Knechtle, A. Wirth & P. Knechtle

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

    B. Knechtle, T. Rosemann & O. Senn

Authors
  1. B. Knechtle
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  2. A. Wirth
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  3. P. Knechtle
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  4. T. Rosemann
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  5. O. Senn
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Corresponding author

Correspondence to B. Knechtle.

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Knechtle, B., Wirth, A., Knechtle, P. et al. Do ultra-runners in a 24-h run really dehydrate?. Ir J Med Sci 180, 129–134 (2011). https://doi.org/10.1007/s11845-010-0500-8

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  • DOI: https://doi.org/10.1007/s11845-010-0500-8

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