Thermoregulation, pacing and fluid balance during mass participation distance running in a warm and humid environment
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Deep body temperature (T c), pacing strategy and fluid balance were investigated during a 21-km road race in a warm and humid environment. Thirty-one males (age 25.3 ± 3.2 years; maximal oxygen uptake 59.1 ± 4.2 ml kg−1 min−1) volunteered for this study. Continuous T c responses were obtained in 25 runners. Research stations at approximately 3-km intervals permitted accurate assessment of split times and fluid intake. Environmental conditions averaged 26.4°C dry bulb temperature and 81% relative humidity. Peak T c was 39.8 ± 0.5 (38.5–40.7) °C with 24 runners achieving T c > 39.0°C, 17 runners ≥39.5°C, and 10 runners ≥40.0°C. In 12 runners attaining peak T c ≥ 39.8°C, running speed did not differ significantly when T c was below or above this threshold (208 ± 15 cf. 205 ± 24 m min−1; P = 0.532). Running velocity was the main significant predictor variable of ∆T c at 21 km (R 2 = 0.42, P < 0.001) and was the main discriminating variable between hyperthermic (T c ≥ 39.8°C) and normothermic runners (T c < 39.8°C) up to 11.8 km. A reverse J-shaped pacing profile characterised by a marked reduction in running speed after 6.9 km and evidence of an end-spurt in 16 runners was observed. Variables relating to fluid balance were not associated with any T c parameters or pacing. We conclude that hyperthermia, defined by a deep body temperature greater than 39.5°C, is common in trained individuals undertaking outdoor distance running in environmental heat, without evidence of fatigue or heat illness.
KeywordsCore temperature Hyperthermia Hydration Fatigue Performance
The authors express their thanks to the volunteers for their participation. We also thank HQ Commandos and HQ Signal (4th Singapore Armoured Brigade) of the Singapore Armed Forces for their participation and support in this research. Finally, we would like to thank Margaret Yap, Teo Ya Shi, Sharon Sng, Chia Ee Von, Jacinta Yeo, David Fan, Priscilla Fan, Grace Teo, Caleb Gan, Joselin Lim, Soh Boon Kee, Evania Tan, Lydia Law, Ian Ng and the student volunteers from ITE College East for their role in data collection. We are grateful to Dr Raija Laukkanen at Polar Electro Oy, Kempele, Finland, for donating the Polar RS800sd running computer. Dr Chris Byrne was supported by an international outgoing short visit grant from the Royal Society, UK.
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