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Core temperature and hydration status during an Ironman triathlon

2006; BMJ; Volume: 40; Issue: 4 Linguagem: Inglês

10.1136/bjsm.2005.022426

1473-0480

Paul B. Laursen, Robert Suriano, Marc J. Quod, Hyunjung Lee, Chris R. Abbiss, Kazunori Nosaka, David T. Martin, David J. Bishop,

Muscle metabolism and nutrition

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.