Comparison of sweat loss estimates for women during prolonged high-intensity running.
OBJECTIVE
This study evaluated the error produced by four commonly used field estimates and two prediction equations of total body sweat loss.


METHODS
Eight women distance runners were studied during a 30-km treadmill run (approximately 70% .VO(2max)) in a warm (30 degrees C T(db)) and a cool (14 degrees C T(db)) environment. Total sweat loss (TSL) was determined from changes in body mass corrected for fluid intake (FI), urine losses (UL), clothing (trapped sweat, TS), CO(2)-O(2) exchange (metabolic mass loss, MML), and respiratory water loss (RWL). TSL was compared with four estimates of sweat losses (often employed in the field) from body mass changes corrected for: a) FI only (F-1); b) FI and TS (F-2); c) FI and UL (F-3); or d) FI, TS, and UL (F-4). Two prediction equations were used also for comparison to TSL values.


RESULTS
In the warm environment, F-1, F-3, and F-4 accurately estimated (0.2-6.9%; P > 0.05) TSL, whereas F-2 produced a large error (15.3%; P < 0.05). In the cool environment, all four estimates produced large errors (14-41%; P < 0.05). Both prediction equations markedly underestimated (20-22%) TSL in the warm environment and underestimated (41%) or overestimated (20%) TSL in the cool environment.


CONCLUSIONS
TSL can be accurately estimated from changes in body mass using F-1, F-3, or F-4 methods in hot environments; however, none of the methods accurately estimated actual TSL values in a cool environment. Neither prediction equation provided accurate estimates of TSL in warm or cool conditions for women runners. These results illustrate the difficulty of accurately estimating and predicting sweat losses in the field.
Cheuvront
Samuel N
SN
Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA, USA.
Haymes
Emily M
EM
Sawka
Michael N
MN
D000328:Adult; D000704:Analysis of Variance; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D010101:Oxygen Consumption / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion; D011237:Predictive Value of Tests; D011336:Probability; D011446:Prospective Studies; D012016:Reference Values; D012129:Respiratory Function Tests; D012420:Running / Q000502:physiology*; D013546:Sweating / Q000502:physiology*; D013997:Time Factors; D014882:Water-Electrolyte Balance / Q000502:physiology