Thermoregulation, pacing and fluid balance during mass participation distance running in a warm and humid environment.
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 degrees C dry bulb temperature and 81% relative humidity. Peak T(c) was 39.8 +/- 0.5 (38.5-40.7) degrees C with 24 runners achieving T(c) > 39.0 degrees C, 17 runners > or = 39.5 degrees C, and 10 runners > or = 40.0 degrees C. In 12 runners attaining peak T(c) > or = 39.8 degrees 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) > or = 39.8 degrees C) and normothermic runners (T(c) < 39.8 degrees 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 degrees C, is common in trained individuals undertaking outdoor distance running in environmental heat, without evidence of fatigue or heat illness.
Lee
Jason K W
JK
Military Physiology Laboratory, Defence Medical and Environmental Research Institute, DSO National Laboratories, 27 Medical Drive, #09-01, Singapore, 117510, Singapore. lkaiwei@dso.org.sg
Nio
Amanda Q X
AQ
Lim
Chin Leong
CL
Teo
Eunice Y N
EY
Byrne
Christopher
C
D000328:Adult; D001481:Basal Metabolism / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D005221:Fatigue / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D008297:Male; D012420:Running / Q000502:physiology*; D013997:Time Factors; D014882:Water-Electrolyte Balance / Q000502:physiology*