ORIGINAL ARTICLE

Core temperature and hydration status during an Ironman triathlon

P B Laursen¹, R Suriano², M J Quod³, H Lee³, C R Abbiss¹, K Nosaka¹, D T Martin³, D Bishop²

¹ School of Exercise, Biomedical and Health Sciences, Edith Cowan University, Joondalup, WA, Australia
² School of Human Movement and Exercise Science, University of Western Australia, Perth, WA, Australia
³ Department of Physiology, Australian Institute of Sport, Canberra, ACT, Australia

Correspondence to:
Correspondence to:
Dr Laursen
School of Exercise, Biomedical and Health Sciences, Edith Cowan University, Building 19, Room 162, 100 Joondalup Drive, Joondalup, WA, Australia 6027; p.laursen{at}ecu.edu.au

Background: Numerous laboratory based studies have documented that aggressive hydration strategies (1–2 litres/h) are required to minimise a rise in core temperature and minimise the deleterious effects of hyperthermia on performance. However, field data on the relations between hydration level, core body temperature, and performance are rare.

Objective: To measure core temperature (T_core) in triathletes during a 226 km Ironman triathlon, and to compare T_core with markers of hydration status after the event.

Method: Before and immediately after the 2004 Ironman Western Australia event (mean (SD) ambient temperature 23.3 (1.9)°C (range 19–26°C) and 60 (14)% relative humidity (44–87%)) body mass, plasma concentrations of sodium ([Na⁺]), potassium ([K⁺]), and chloride ([Cl^–]), and urine specific gravity were measured in 10 well trained triathletes. T_core was measured intermittently during the event using an ingestible pill telemetry system, and heart rate was measured throughout.

Results: Mean (SD) performance time in the Ironman triathlon was 611 (49) minutes; heart rate was 143 (9) beats/min (83 (6)% of maximum) and T_core was 38.1 (0.3)°C. Body mass significantly declined during the race by 2.3 (1.2) kg (–3.0 (1.5)%; p<0.05), whereas urine specific gravity significantly increased (1.011 (0.005) to 1.0170 (0.008) g/ml; p<0.05) and plasma [Na⁺], [K⁺], and [Cl^–] did not change. Changes in body mass were not related to finishing T_core (r = –0.16), plasma [Na⁺] (r = 0.31), or urine specific gravity (r = –0.37).

Conclusion: In contrast with previous laboratory based studies examining the influence of hypohydration on performance, a body mass loss of up to 3% was found to be tolerated by well trained triathletes during an Ironman competition in warm conditions without any evidence of thermoregulatory failure.

Keywords: dehydration; sodium; hyponatraemia; fluid replacement; urine specific gravity

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Commentary

K Sharwood⁴

⁴ UCT/MRC Research Unit for Exercise Science and Sports Medicine, University of Cape Town, Cape Town, South Africa; sharwood{at}sports.uct.ac.za

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Commentary

T Noakes⁵

⁵ Human Biology, University of Cape Town, Cape Town, South Africa; tdnoakes{at}sports.uct.ac.za

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