Water immersion in the treatment of exertional hyperthermia: physical determinants.
OBJECTIVE
We examined the effect of differences in body surface area-to-lean body mass ratio (AD/LBM) on core temperature cooling rates during cold water immersion (CWI, 2°C) and temperate water immersion (TWI, 26°C) after exercise-induced hyperthermia.


METHODS
Twenty male participants were divided into two groups: high (315.6 ± 7.9 cm·kg, n = 10) and low (275.6 ± 8.6 cm·kg, n = 10) AD/LBM. On two separate occasions, participants ran on a treadmill in the heat (40.0°C, 20% relative humidity) wearing an impermeable rain suit until rectal temperature reached 40.0°C. After exercise, participants were immersed up to the nipples (arms remained out of the water) in either a CWI (2°C) or a TWI (26°C) circulated water bath until rectal temperature returned to 37.5°C.


RESULTS
Overall rectal cooling rates were significantly different between experimental groups (high vs low AD/LBM, P = 0.005) and between immersion conditions (CWI vs TWI, P < 0.001). Individuals with a high AD/LBM had an approximately 1.7-fold greater overall rectal cooling rate relative to those with low AD/LBM during both CWI (high: 0.27°C·min ± 0.10°C·min vs low: 0.16°C·min ± 0.10°C·min) and TWI (high: 0.10°C·min ± 0.05°C·min vs low: 0.06°C·min ± 0.02°C·min). Further, the overall rectal cooling rates during CWI were approximately 2.7-fold greater than during TWI for both the high (CWI: 0.27°C·min ± 0.10°C·min vs TWI: 0.10°C·min ± 0.05°C·min) and the low (CWI: 0.16°C·min ± 0.10°C·min vs TWI: 0.06°C·min ± 0.02°C·min) AD/LBM groups.


CONCLUSIONS
We show that individuals with a low AD/LBM have a reduced rectal cooling rate and take longer to cool than those with a high AD/LBM during both CWI and TWI. However, CWI provides the most effective cooling treatment irrespective of physical differences.
Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON, CANADA.
Brian J
BJ
Friesen
Mike R
MR
Carter
Martin P
MP
Poirier
Glen P
GP
Kenny
D050154:Adiposity / Q000502:physiology; D000328:Adult; D015992:Body Mass Index; D001830:Body Surface Area; D001831:Body Temperature; D003080:Cold Temperature / Q000009:adverse effects; D004947:Esophagus / Q000502:physiology; D005334:Fever / Q000209:etiology / Q000628:therapy*; D006358:Hot Temperature; D006801:Humans; D007101:Immersion; D008297:Male; D005082:Physical Exertion / Q000502:physiology*; D012007:Rectum / Q000502:physiology; D012420:Running / Q000502:physiology; D013997:Time Factors; D014867:Water; D055815:Young Adult
D014867:Water